Open MAN page in Gnome Yelp if an X Session is Running

Toss this in your ~/.bashrc to use the Gnome Yelp help viewer to open a man page.  This replaces the man command with a function and only uses the CLI version of man if there’s no running X session.

If an X session is running it instead opens the man page in Yelp as a background job so you can keep working in your shell while Yelp is open.