add git commands for submitting pull request

I am not sure how much detail is appropriate here (or if there should be a FAQ as in the bc/README.md), but these are some notes I took when helping a new git user submit a pull request.

I also removed redundant text about "if it is easier ... please mail us"
this  `<meaningful-name>` serves the dual purpose of getting newcomers used to the `<insert-text-here>` convention.