Improve GitHub mirroring instructions

docs/github-mirror.md

 # How to add a mirror to GitHub
 
+## GitLab side
+
 If you want to mirror your repository "myproject" from gitlab.archlinux.org to the github.com/archlinux organization,
 you should create an empty project for your project at github.com/archlinux/myproject or
 if that's an existing repository, make sure that the current histories of the source and
@@ -18,6 +20,8 @@ and then click Mirror repository.
 
 A new entry will pop up which has a button titled "Copy SSH public key". Click that.
 
+## GitHub side
+
 Then go to https://github.com/archlinux/myproject/settings/keys and add a new deploy key.
 Give it the title "gitlab.archlinux.org" so we know where it's from and then paste the
 public key you copied from GitLab just now. Check "Allow write access" and
@@ -25,6 +29,16 @@ click "Add key".
 
 Your push mirror should now work.
 
+### GitHub repo settings
+
+In the repo settings on GitHub's side you should disable a few things to clean up the project page:
+
+- GitHub Actions
+- Wikis
+- Issues
+- Projects
+
 Finally, in the GitHub description of the mirrored project, append " (read-only mirror)"
 so that people know it's a mirror. Also, in the website field put the full URL to the
-upstream repo on our GitLab.
+upstream repo on our GitLab, and disable "Packages" and "Environments" from being shown on the
+main page.