Add retirement banner to wiki.gnome.org
As part of the planned retirement of wiki.gnome.org, we agreed that we need to add a banner to the top of all the wiki pages, to announce the retirement. The banner just needs to be This site is planned for retirement ‒ see the <a href="https://hedgedoc.gnome.org/wiki-migration-guide#">migration guide</a>
, and could look like this:
We previously spoke about having a web developer provide some code for this, but I'm not sure what exactly is required. If you can provide any more details, that would be great.