The HA docs already have a link to their github source (“Edit this page on github”), but not everyone is good at git and not everyone will know that an edit link will allow them to see version info/history there.
Following a discussion elsewhere here I propose generating the date or commit number (or some other versioning info) of the doc page on the page. This would presumably involve minimal/one off programming as the pages are automatically generated. Therefore one code change should be able to generate every page with a bit of extra info.
Idea extension: link to last two or three versions.