Useful_scripts.rst formatting fix

Fixes syntax and formatting in useful_scripts.rst

 * Remove whitespace at the end of lines
 * Remove 2 accidentally added _
 * Add `` around Submission.all_comments
 * Reformat to keep within 80 chars pr line

Also added another small commit that adds a direct link to the github page, so it becomes that much easier for people to add their own scripts to the list.