Document how to re-create the MyST Parser purely with markdown-it-py

[choldgraf]

In a recent conversation we discussed how someone could build a MyST Parser from scratch within Python. @chrisjsewell noted that because MyST is built on markdown-it-py, this would be a fairly trivial task and listed the Python code that would be needed:

#342 (comment)

We should document this in the myst docs so that users can see how straightforward this is!

[damianavila]

Assigning myself since I was looking at this in my investigation about the parser and I think I can now take a stab on it 😉

[damianavila]

Well, actually I can not assign myself because I do not have permission, it seems, @choldgraf can you add me as an assignee? Thanks!

[choldgraf]

Done! Hmm I need to figure out what kinds of permissions to give the @executablebooks/ebpteam to allow this