Run documentation on main

Previously, the "docs" action was run only on pull requests. This means
that documentation is not generated and deployed when the commit reaches
main, leading to stale github pages. This commit ensures that
documentation is also run on main.

Author: Sbozzolo

.github/workflows/docs.yml

@@ -2,6 +2,10 @@ name: Documentation
 
 on:
   pull_request:
+  push:
+    branches:
+      - main
+    tags: '*'
 
 jobs:
   docbuild: