Add an optional scope to git messages

[drazik]

I think adding a scope is very informative in some commit messages. To use an example from our current guidelines, I think this commit message:

fix(contacts): A too long list breaks the scrolling

is way more informative than the version without the scope:

fix: A too long list breaks the scrolling

The fact that this refers to the contacts list can be written in the body, but I think that's not the place for such an information.

Also, this is a good help to write changelogs (manually or automatically). semantic-release uses it, for example.

Obviously, sometimes this scope doesn't add any information, so it must be optionnal.

See https://conventionalcommits.org/#spec-item-4 for more informations about the scope in the conventional commits specification, which widely inspired udacity.

What do you think about it ?

[ptbrowne]

Yes please. I use it occasionally :)

[gregorylegarec]

I do not use scope in a regular basis but if some of us use to, let's add it to the guidelines.