Add contribution notes as markdown documents (#8)

These documents will help possible developers from the community to
start developing for and contributing to this project.

docs/CONTRIBUTING.md

@@ -0,0 +1,52 @@
+# Welcome to the Contributing Guide for the cppIni project!
+
+We are very happy that you are interested in contributing to cppIni.
+
+This document will provide you with all the information you need to get started.
+
+## Issues
+
+If you find a bug, please open an issue on the GitHub issue tracker. Please make sure that there is no existing issue
+for your problem/feature request. If there is an existing issue, please add a comment to the existing issue instead of
+creating a new one.
+If you are providing a bug report, please make sure to include the following information:
+
+- The version of cppIni you are using
+- The compiler you are using
+- The operating system you are using
+- A minimal example that reproduces the bug
+- A description of the expected behavior and the actual behavior
+
+Feature requests are no bug reports, therefore please don't open an issue for a feature request. Instead, please open a
+pull request with your feature. Feature requests that are opened as issues will be closed without further notice.
+
+## Pull Requests
+
+If you want to contribute code to cppIni, please open a pull request on GitHub. Please make sure that there is no
+existing pull request for your changes. If there is an existing pull request, please add a comment to the existing pull
+request instead of creating a new one. Pull requests have to be reviewed by at least one maintainer before they can be
+merged. On top of that, all CI builds have to pass.
+
+Please make sure that your pull request follows the following guidelines:
+
+- All pull request have to be based on the `develop` branch
+- The pull request has a meaningful title and description
+- The pull request is linked to an issue (if applicable)
+- The code is documented according to the [Doxygen Style Guide](https://www.doxygen.nl/manual/docblocks.html)
+- The code is tested
+- There is no merge commit from develop to the pull request's branch
+    - If you want to update your branch, please rebase it on the current develop branch prior to opening the pull
+      request
+    - If there is a merge conflict due to another pull request being merged in the meantime, merge commits are permitted
+
+If your code is not ready to be reviewed yet, please open it as a draft pull request.
+
+## Code of Conduct
+
+Please note that this project is released with a Contributor Covenant Code of Conduct. By participating in this project
+you agree to abide by its terms. See [CODE_OF_CONDUCT.md](CODE_OF_CONDUCT.md) for more information.
+
+## License
+
+By contributing to cppIni, you agree that your contributions will be licensed under its GPLv3 license.
+See [LICENSE](LICENSE) for more information.