docs: Add dev install steps

backend/CONTRIBUTING.md

@@ -11,7 +11,33 @@ This directory contains the code files that define the Flask backend API app. Th
 - `blueprints/` contains the app code. See: [Modular Applications with Blueprints](https://flask.palletsprojects.com/en/2.3.x/blueprints/)
 - `tests/`  contains unit tests. See [Testing Flask Applications](https://flask.palletsprojects.com/en/3.0.x/testing/)
 - `pyproject.toml` specifies the [Python package](https://packaging.python.org/)
-- `MANIFEST.in` tells the build system what [other files to include](https://setuptools.pypa.io/en/latest/userguide/miscellaneous.html#controlling-files-in-the-distribution) (such as the static files)
+- `MANIFEST.in` tells the build system what [other files to include](https://setuptools.pypa.io/en/latest/userguide/miscellaneous.html#controlling-files-in-the-distribution) (such as the static files)
+
+## Installation
+
+To create a virtual environment
+
+```bash
+python -m venv .venv
+```
+
+Activate the environment
+
+```bash
+# Linux
+source .venv/bin/activate
+
+# Windows
+.venv\Scripts\activate
+```
+
+To install the package in [editable mode](https://pip.pypa.io/en/stable/topics/local-project-installs/#editable-installs):
+
+```bash
+pip install --editable ./backend
+```
+
+## Usage
 
 To run the app in development mode: