Perhaps we should just encourage extensions to include an optional "docs" folder ???
That way, the ext author could elect to include a README.txt with instructions on how to get the extension set up/configured in the board, or how to use it in the board itself, etc. Really, any sort of Author Notes / DIY Notes similar to what MODX allowed could be put in a README.
They could also add other documentation they may want as well, such as:
CHANGELOG.txt (another item available in MODX but missing from extensions)
EVENTS.txt file if they added events to their extension and want to document them for other users
FAQ.txt if they feel it necessary to provide one
etc...
It would also allow some authors to get really creative and create a "branded" README.html for example, with their own styling, graphics and logos and other fun stuff!
Also, in certain common support requests, the author may be able to simply refer them to the DOCs folder