Add section about commit style
Add section about commit style

We would like to understand the reason behind the change in the future.
Using this kind of style makes it easier to use tools like `git log` and
the like.

dg-ratiodata/aruba,dg-ratiodata/aruba,maxmeyer/aruba,mvz/aruba,cucumber/aruba,dg-ratiodata/aruba,dg-ratiodata/aruba,maxmeyer/aruba,mvz/aruba