[dev] Reminder about submitting code

[Donald Sharp]

All -

I am seeing a large number of PR's lately that have some completely
inconsistent tab/spacing that just look awful.  I would highly
recommend everyone install the git `clang-format`.  This is documented
in our workflow:

http://docs.frrouting.org/projects/dev-guide/en/latest/workflow.html#code-formatting

Please take a second and set yourself up and take advantage of this fine tool.

thanks!

donald