Revise the guide with my learnings

Extend the guide a good bit, encouraging more workshops.  Also copyedit the whole document.
Link Doodle

Add a link to Doodle for convenience.
Update numbers on no-show rate

Ben supplied that number in his review.
Link quick introduction
Mention CLGs in addition to Learners Meetups
Merge pull request #126 from lehmannro/patch-1

Revise the guide with my learnings