Add a "before you go" page

[klieret]

Should use the last page/episode to advertise for HSF Training and also tell them to maybe star the repositories. This should be a general file that we could create centrally via _includes/

[stale]

This issue or pull request has been automatically marked as stale because it has not had recent activity. Please manually close it, if it is no longer relevant, or ask for help or support to help getting it unstuck. Let me bring this to the attention of @klieret @wdconinc @michmx for now.