☂️ Migrate RST docs to Markdown - ongoing good first issue

See original GitHub issue

☂️ This is an epic / umbrella issue We expect this to be done in multiple PRs as it’s better to change a few pages at a time, please reference this issue in any new PRs

Description

In early 2021 Wagtail began the move to Markdown documentation instead of RST (ReStructured Text) to make it easier for new developers to get started with the docs.
Our goal is to migrate all documentation to Markdown (.md) files.
If you want to contribute to these efforts it is a great way to get started with Wagtail contributions as you get to read the documentation and learn about our PR process.

How to work on this

First, pick a section you feel you can migrate, see the list below, add a comment to this issue with what area you are keen to work on.
Be sure to read the latest docs on how to use the markdown syntax - https://docs.wagtail.org/en/latest/contributing/documentation_guidelines.html
A nice to have, but not required, is to also format the resulting markdown file with prettier, this can be done by commenting out the .md temporarily in the .prettierignore file and also updating the package.json formatting script by adding .md - then run your formatting on the files changed. Be sure not to commit the changes to the prettier config or package file though.
see the related PRs below for references to how this has been done for some parts of the docs already.