Add reference to _episodes for lesson contribution

Hi,

I added a reference to the _episodes directory where the lesson material is located. As a novice (sort of) to github, it was quite difficult to figure out how to contribute. Hope this helps future contributors.

Adding structure to instructor guides/notes

Updated setup instructions to reflect new GitHub interface & changes to template

Updated the setup instructions to reflect the current GitHub interface,
and small changes to the lesson template files.

Adding accessibility changes from swcarpentry/styles

Merge branch 'gh-pages' of https://github.com/swcarpentry/styles into gh-pages to accommodate accessibility changes

Fix display of double curlies using {% raw %}

Fix broken link to training memory lesson

accessibility fixes.

fix search meta tag.

Add label to search box and navigation arrows.

1. Checking that `index.md` has `root` set to '.'
2. Checking that `_config.yml` has `root` set to '..'

Adding link to syllabus (episodes) from setup instructions

Mention that R packages are needed to build example lesson.

1.  Adding link using `page.root`.
2.  Adding ID attribute to syllabus.

Replaces #56.

fixing name of lesson_initialize.py script in point 11

Disambiguating "guides"

Adding a footnote to the schedule that it may vary.