Add note about live editing of content through gollum
Launch gollum with --live-preview and on current branch

Also cleaned up the start/stop scripts for gollum so they
automatically add the correct branch, better detection
of the gollum pid, and better messages so you can see what's
happening with gollum processes.
Link to sections of "Developing on Windows"

Also did some cleanup of various spelling and grammatical errors
as I went.

Fixes XWALK-477