website: Updated to 72 char git description width

This commit updates the contribution guide to change the git commit
description width to 72 characters. It was previously 75 characters.
This is non-standard and was causing formatting issues on Gerrit.

Corresponding update in the file:

Change-Id: Ia4adccfb534c24c92e3b2959563354478237894c
Reviewed-by: Jason Lowe-Power <>
Maintainer: Jason Lowe-Power <>
Tested-by: Jason Lowe-Power <>
2 files changed