[#6896] Contributing guide for new devs

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>
[#6896] Add license header

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>
[#6896] Update test example; comment merge instructions

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>