Adding Codespaces Documentation (#1144)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>
Co-authored-by: Pradyun Gedam <pradyunsg@gmail.com>
Co-authored-by: Brett Cannon <brett@python.org>

getting-started/setup-building.rst

@@ -655,3 +655,72 @@ every rule.
 
 
 .. _issue tracker: https://github.com/python/cpython/issues
+
+
+.. _using-codespaces:
+
+Contribute using GitHub Codespaces
+==================================
+
+.. _codespaces-whats-codespaces:
+
+What is GitHub Codespaces?
+--------------------------
+
+If you'd like to start contributing to CPython without needing to set up a local
+developer environment, you can use
+`GitHub Codespaces <https://github.com/features/codespaces>`_.
+Codespaces is a cloud-based development environment offered by GitHub that
+allows developers to write, build, test, and debug code directly within their
+web browser or in Visual Studio Code (VS Code).
+
+To help you get started, CPython contains a
+`devcontainer folder <https://github.com/python/cpython/tree/main/.devcontainer>`_
+with a JSON configuration file that provides consistent and versioned codespace
+configurations for all users of the project. It also contains a Dockerfile that
+allows you to set up the same environment but locally in a Docker container if
+you'd prefer to use that directly.
+
+.. _codespaces-create-a-codespace:
+
+Create a CPython codespace
+--------------------------
+
+Here are the basic steps needed to contribute a patch using Codespaces.
+You first need to navigate to the
+`CPython repo <https://github.com/python/cpython>`_ hosted on GitHub.
+
+Then you will need to:
+
+1. Press the ``,`` key to launch the codespace setup screen for the current
+   branch (alternatively, click the green :guilabel:`Code` button and choose
+   the ``codespaces`` tab and then press the
+   green :guilabel:`Create codespace on main` button).
+2. A screen should appear that lets you know your codespace is being set up.
+   (Note: Since the CPython devcontainer is provided, codespaces will use the
+   configuration it specifies.)
+3. A `web version of VS Code <https://vscode.dev/>`_ will open inside your web
+   browser, already linked up with your code and a terminal to the remote
+   codespace where CPython and its documentation have already been built.
+4. Use the terminal with the usual Git commands to create a new branch, commit
+   and push your changes once you're ready!
+
+If you close your repository and come back later you can always resume your
+codespace by navigating to the CPython repo, selecting the codespaces tab and
+selecting your most recent codespaces session. You should then be able to pick
+up from where you left off!
+
+.. _codespaces-use-locally:
+
+Use Codespaces Locally
+----------------------
+
+On the bottom left side of the codespace screen you will see a green or grey
+square that says :guilabel:`Codespaces`. You can click this for additional
+options. If you prefer working in a locally installed copy of VS Code you can
+select the option ``Open in VS Code``. You will still be working on the remote
+codespace instance, thus using the remote instance's compute power. The compute
+power may be a much higher spec than your local machine which can be helpful.
+
+
+.. TODO: add docker instructions