Specify commit message format

[davidB]

1. add the description of commit message into the contribution guide (to create if it doesn't exist)
2. add a git hook to check the format (and provide short info and links when it rejects if possible)

check that commit message follow the format like

<gitmoji> ticket_num_opt (scope_opt) summary

longer_description_opt

sample: https://github.com/git/git/blob/master/templates/hooks--commit-msg.sample