📖 Remove RTD and add Netlify

[choldgraf]

This removes our ReadTheDocs configuration and adds Netlify configuration, because this was much easier and more reliable in getting our docs previews running.

It also:

• Move environment.yml to requirements.txt (since installing with pypi has less overhead than conda)
• Adds an example of markdown-based computation

[netlify]

👷 Deploy Preview for mystmd processing.

Name	Link
🔨 Latest commit	0e3c51d
🔍 Latest deploy log	https://app.netlify.com/sites/mystmd/deploys/66202d315f93bc0008401d2b

[LecrisUT]

A quick comment, RTD workflow parts, I will comment in a separate PR. It would be nice to add badges and CI checks on the main branch to show the new users how they can setup Netlify (and RTD in the future) to work with mystmd

[choldgraf]

I believe that @rowanc1 has already added instructions on how to deploy to netlify here!

https://mystmd.org/guide/deployment-netlify

[LecrisUT]

Indeed, but I think having badges and connecting the Github action for the main branch would also be important to document even if redundant. RTD is quite a common workflow for users of myst-parser and it would be nice to have it documented how they can get similar results in the other hosting providers that (currently) work well with mystmd