This should ensure that it will be included at the very end of the
configuration, allowing it to override any other options in the file.
Not sure that I _really_ need it, but it's tidier this way.
I want to be able to re-use it between different source control systems
(e.g: `jj`).
As a first step, extract it to a proper module so that I can have it
live in a single space.
