Until now the algorithm would assume that the latest release on
Codeberg is always a final release.
There is the very real possibility of prereleases, which we've learned
today, but we can easily use jq to filter these out.
This relates to #19 and fixes#20.
This adds a workflow and accompanying script to update readable.css. The
script gets the latest tag version from the readable.css repository on
codeberg.org and compares it to the currently used version. If the
versions don't match up, we download readable.css and readable.min.css
from Codeberg and update layouts/partials/head.html.