contributing: commit message

At RERO we've just noticed that there's still an old example of commit message in the `CONTRIBUTING.rst` file:

```
6. Commit your changes and push your branch to GitHub:

.. code-block:: console

$ git add .
$ git commit -s
-m "component: title without verbs"
-m "* NEW Adds your new feature."
-m "* FIX Fixes an existing issue."
-m "* BETTER Improves and existing feature."
-m "* Changes something that should not be visible in release notes."
$ git push origin name-of-your-bugfix-or-feature
```
As far as I understand, commit message recommendations has changed: https://github.com/inveniosoftware/invenio/blob/master/CONTRIBUTING.rst#commit-messages

Should the cookiecutter template be updated accordingly?

Start with CONTRIBUTING.rst and compare its commit-message example with the linked Invenio CONTRIBUTING.rst guidance. Update the outdated example in the cookiecutter template so it reflects the current recommendations, then verify that the resulting instructions are consistent.

Written by the indexing model from the issue text.