contrib: Simplify the command to create a feature branch.

You can create a work branch off origin/master by simply running:

$ git checkout -b my-feature origin/master

BUG=None
R=borenet@google.com
NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=1057513004

Review URL: https://codereview.chromium.org/1057513004
1 file changed