Update CONTRIBUTING documentation
Update CONTRIBUTING documentation

Changes:
    - Added reference link to the formatting commit message page

Tested:
    Not applicable, as this is a documentation change.

Change-Id: I9a130b8f9ab40d98302a8ac702c4a4d714378063
Signed-off-by: George Keishing <bef0a9ecac45fb57611777c8270153994e13fd2e@in.ibm.com>

openbmc/openbmc-test-automation,openbmc/openbmc-test-automation