Add License and contributing.md; update acknowlegements

CONTRIBUTING.md

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+# Contributing to the lecture notes
+
+Contributions are welcome to improve these lecture notes! Whether you want to fix typos, improve explanations, or suggest new content, your help is appreciated.
+
+Please follow the steps below to contribute.
+
+## How to Contribute
+
+### Reporting Issues
+
+If you find an issue with the lecture notes (such as a typo, unclear explanation, or missing information), please open a new issue in the GitHub repository. You can do this by:
+1. Navigating to the [Issues page](https://github.com/EricWay1024/Homological-Algebra-Notes/issues).
+2. Clicking "New issue."
+3. Providing a clear description of the issue and, if possible, a suggested fix.
+
+In your issue, please indicate which version of the notes you are viewing by stating the date on the first page and whether it is the black-and-white or colour version.
+
+### Making a Pull Request
+
+1. **Fork the repository**: Click the "Fork" button at the top right of this page to create your own copy of the repository.
+
+2. **Clone your fork**: Clone your fork to your local machine using the following command:
+   ```bash
+   git clone https://github.com/[YourUserName]/Homological-Algebra-Notes.git
+   cd Homological-Algebra-Notes
+   ```
+    where you need to replace `[YourUserName]` with your GitHub user name.
+3. **Create a branch**: Create a new branch for your changes:
+    ```bash
+    git checkout -b fix-typo
+    ```
+4. **Make your changes**: Edit the Typst files (`main.typ`, etc.). Make sure your changes are clear and well-organised.
+5. **Commit your changes**: After making the changes, commit them to your branch:
+    ```bash
+
+    git add .
+    git commit -m "Fix typo in Section 2.1"
+    ```
+    Replace the commit message with a brief description of what has been changed.
+6. **Push to your fork**: Push your changes to your forked repository:
+    ```bash
+    git push origin fix-typo
+    ```
+7. **Create a pull request**: Once your changes are pushed, navigate to the original repository and open a pull request (PR). Describe the changes you made and why they are important.

LICENSE

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+Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
+
+Copyright (c) 2024 Yuhang Wei
+
+Authors:
+- Notes by Yuhang Wei
+- Lectures by Kobi Kremnitzer
+- Partially Based on Previous Notes by Sebastian Monnet
+
+You are free to:
+- Share — copy and redistribute the material in any medium or format.
+- Adapt — remix, transform, and build upon the material for any purpose, **non-commercially**.
+
+As long as you follow these license terms:
+- Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
+
+You may not:
+- Use the material for commercial purposes.
+
+For more details, see: https://creativecommons.org/licenses/by-nc/4.0/

README.md

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-# Lecture Notes for University of Oxford course C2.2 Homological Algebra (Michaelmas, 2023-24)
+# C2.2 Homological Algebra - Lecture notes
 
-Go to [Release](https://github.com/EricWay1024/Homological-Algebra-Notes/releases) for the latest compiled PDF, both the colourful (for screen viewing) and not-so-colourful version (for printing).
+This repository contains the lecture notes for the course C2.2 Homological Algebra at the Mathematical Institute, University of Oxford, based on what was delivered during the Michaelmas term of the 2023-24 academic year by Prof. Kobi Kremnitzer. These notes are partially based on a previous version by Sebastian Monnet.
 
-Written with [Typst](https://typst.app/).
-To compile and watch for changes:
-```
-typst watch main.typ
-```
+## Find the latest version of PDFs
 
-Also check out [this repo of mine](https://github.com/EricWay1024/tikzcd-editor) for drawing commutative diagrams in Typst.
+Go to [Release](https://github.com/EricWay1024/Homological-Algebra-Notes/releases) for the latest compiled PDF, both the colour (for screen viewing) and black-and-white version (for printing). Note that the black-and-white version still contains some diagrams with colourful labels.
 
-Any issues and pull requests are welcome.
+## How to Contribute
+
+Contributions are welcome! These notes are supposed to be constantly updated, and that requires collaborative efforts. If you find a typo, error, or have suggestions for improvement, feel free to submit a pull request. You can also open an issue to report any problems or ask questions. Please refer to [CONTRIBUTING.md](CONTRIBUTING.md) for further instructions on how to contribute. 
+
+If you make any contribution, you will be mentioned in the acknowledgements below. Please indicate your preferred name when opening an issue or making a pull request. Your GitHub user name will be used in a lack of a preferred name.
+
+## Acknowledgements
+
+This project relies on the support and collaboration of the following individuals:
+
+- Prof Kobi Kremnitzer for delivering the lectures and adopting these notes as a course material;
+-  Sebastian Monnet for creating the previous version of these notes;
+- Qixuan Fang for reading the first drafts of the notes and offering feedback;
+-  [Quanwen Chen](https://github.com/Steven1677) for contributing to the GitHub workflows; and
+-  [@hbghlyj](https://github.com/hbghlyj), [@JuliaScythe](https://github.com/JuliaScythe), [@ascchrvalstr](https://github.com/ascchrvalstr) for pointing out various typos.
+
+## How to Compile the Notes
+
+These lecture notes are written using [Typst](https://typst.app/), a modern typesetting system. To compile the notes and watch for changes, follow these steps:
+
+1. **Install Typst**: You can download and install Typst from [here](https://typst.app/download) (if you haven't already).
+
+2. **Clone the repository**:
+   ```bash
+   git clone https://github.com/EricWay1024/Homological-Algebra-Notes.git
+   cd Homological-Algebra-Notes
+   ```
+
+3. **Compile the notes**: To compile and watch for changes in the main Typst file (usually main.typ), run the following command:
+    ```
+    typst watch main.typ
+    ```
+
+This will compile the file and automatically regenerate the output every time you save changes.
+
+## Related Project
+
+Check out [this repo of mine](https://github.com/EricWay1024/tikzcd-editor) for drawing commutative diagrams in Typst.
+
+## License
+
+This project is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License. You are free to use, share, and remix the material as long as it is not for commercial purposes, and you must provide proper attribution to the original authors.
+
+For more information, see the [LICENSE file](LICENSE) or visit the [Creative Commons website](https://creativecommons.org/licenses/by-nc/4.0/).