Add Documentation For Contributing To CPython Using Github Codespaces

[marlenezw]

Describe the enhancement or feature you'd like
I'd like to add documentation to show how to use Codespaces for CPython using the devcontainer file recently added. There has been some discussion about this issue here and several people mentioned documentation would be helpful.

Describe alternatives you've considered
I've considered adding a page that describes the steps needed to contribute to CPython using Codespaces. I think this should be added under the Getting Started section of the devguide.

Additional context
More information about codespaces can be found here.

[willingc]

Closing since #1144 has landed. Thanks @marlenezw