Remind people to create a new branch

Add a line reminding someone who is creating a fresh project in which to
write docs to create a new branch for their work.
Remove $ from ONE file

In most places within this project $ is _not_ used to indicate
commands at the command prompt,
so I am bringing this file into compliance with that convention.
There are some places where $ is used that I think it may still make
sense (in order to distinguish between commands and output). I'll
discuss that with Daniele before committing.
Explain what some git commands are doing
Improve paragraph flow

Improve the flow of the "learning reStructuredText" paragraph.
Merge pull request #258 from kevindaum/always-branch

Remind people to create a new branch