1.  Cutting "How Learning Works" material from index to instructors' guide.
2.  Putting link to instructors' guide on site home page.
Adding notes to teaching guide
Merge branch 'master' into making-teaching-instructions-more-accessible
Merge pull request #397 from gvwilson/master

Master
Merge branch 'master' of https://github.com/swcarpentry/bc