In order to fix Bug 36437 - A strict and correct Git workflow document is needed one thing we can do is to remove from the Workflow document anything that is not strictly part of the workflow. I already removed the Justification section, and the Git installation instructions could follow. It is a one time action with no MediaWiki-specific steps and there are plenty of sites out there documenting very well how to do this.
Git/Getting started solves this step by simply linking to https://help.github.com/articles/set-up-git . Works for me, and if someone has a better URL we can just use it in addition or as replacement.