Convert documentation into MyST Markdown

[choldgraf]

Description

Our documentation is currently written in rST, but it will be easier for others to maintain and update if we converted it to MyST Markdown.

Guide to implement

The easiest way to do this would be to:

• Ensure all open PRs are not changing the docs (to avoid merge conflicts)
• Run the rst2myst tool on these docs: https://github.com/executablebooks/rst-to-myst