Skill: Pull request and branches, common errors

Beginners Git users often do confusing things when working with pull requests and branches

## Possible levels
- Make changes to a pull request and think they need to submit another for the changes to take effect
- People will base their new pull requests on their old pull requests
- Make new changes on same branch then wonder why they can't make a pull request
- Above, but then they solve the issue by making a new branch

## Assumptions to address
- New branches are based off master
- Changes are automatically pulled in
- Pull requests refer to changes, not branches