Intro & syllabus

This MR modifies the readme, adds a syllabus and base slides to match it.

content/feature_branching.md

-## Feature branching
-
-1. Create a new feature branch called 'squash_some_bugs'
-2. Edit 'bugs.rb' and remove all the bugs.
-3. Commit
-4. Push
-5. Commands
-
-----------
-```
-git checkout -b squash_some_bugs
-# Edit `bugs.rb`
-git status
-git add bugs.rb
-git commit -m 'Fix some buggy code'
-git push origin squash_some_bugs
-```