Move cherry-picker's readme to readthedocs or something

[Mariatta]

The readme for cherry-picker is getting long. Perhaps we can have documentation hosted in readthedocs or something similar.

[Mariatta]

GitMate.io thinks possibly related issues are python/core-workflow#89 (Change cherry-picker's README to treat it as a package), https://github.com/python/core-workflow/issues/268 ([cherry-picker] [idea 💡] Extend backport sources), python/core-workflow#22 (Move build status to README.rst?), python/core-workflow#249 ([cherry-picker] Document config options), and python/core-workflow#113 (Questions about cherry-picker from Windows never-venv user).

[webknjaz]

I believe that RTD currently works with one docs site per repo and since this one has two projects it might not work out well.

[jaraco]

I'd actually recommend not to publish the readme on RTD. It will add additional workflows and toil to the project, and for what? The readme is already hosted on Github and PyPI. I would suggest maybe separating the changelog out into a separate file. I don't feel super-strongly about it, but in my projects, I only use RTD when there's need for more context (generated content, API docs, etc) with high readership (many docs are fine to be hosted in Github).

[hugovk]

We could use GitHub Pages to publish the README.

It would RST converting to Markdown, but here's a quick demo just by renaming: https://hugovk.github.io/cherry-picker/

I turned it on at https://github.com/hugovk/cherry-picker/settings/pages by selecting main and / (root):

[hugovk]

I'd actually recommend not to publish the readme on RTD. It will add additional workflows and toil to the project, and for what? The readme is already hosted on Github and PyPI. I would suggest maybe separating the changelog out into a separate file. I don't feel super-strongly about it, but in my projects, I only use RTD when there's need for more context (generated content, API docs, etc) with high readership (many docs are fine to be hosted in Github).

I agree with this.

Please see PR #104 to move the changelog to its own file.