footer: correct edit-page URLs

Paths in Hugo are relative to the content-directory, so we need to link
relative to that, otherwise we get an error when trying to edit.

This was missed when porting this from Jekyll to Hugo.
2 jobs for master in 1 minute and 3 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #2686789
pages

00:01:03

 
  Deploy
passed pages:deploy

00:00:02