Add more guidance re: Branches

[DrLynTaylor]

Eg.. Update The 'Get started' page to include.

• It best practice to create an additional branch for each new pull request,
• How to delete your branch, given it says 'You can then delete your branch in your forked repository and sync any other branches with the upstream CAMIS repository', but instructions on how to do would be helpful

[statasaurus]

It doesn't really matter if you make additional branches when you are doing a PR from the forked repo. But we can add instructions for the second thing