Add instructions for git with Plan A

Add MUDE-specific instructions for Plan A (teacher adds content to book and toc). 2 floavors:

  1. VS code (adapt existing insteructions)
  2. GitHub GUI (Mike or Ahmed)

include instructions for named branch (e.g., robert), optionally opening a merge request and tagging a TA for review

can we create groups of people who can be tagged for adding the content? if not, we need a way to quickly identify branches or content for review.....use an Issue and assign someone. add also a line that says "when in doubt, just mention (tag) robert and/or caspar, who will check and delegate"

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information