The git checkout and build process can leave the checkout
date in the tarball release, leading to unstable sorting.
I tried to use `git restore-mtime`, but that doesn't work for
ikiwiki, because dgit interferes with it.
ikiwiki/markdown is a basewiki page and shouldn't link to pages in tips.
Instead, make the tips link to it, so backlinks will point back to them.
While I'm at it, move the info about the emacs mode to a tip.
Simon McVittie
Joey Hess