I would expect that you maintain the github-issues branch as a branch of master, just like we do for branches of cpython master. Rather than 'backport' you occasionally merge upstream/master into github-issues. I don't know if you are using the fork workflow for other repositories or if people just push to python/whatever.

One way to make a formatted (html) version of the alternate available to read would be to check it in, possible into a separate branch. I keep a trailing-whitespace-trimmed copy of idle.html in idlelib so that people can read it from the IDLE menu without being online. (The copy function is in idlelib/help.py.) Git has no problem with html.