More Git guidance

[iaindillingham]

The "How to use Git effectively" page offers links, but not guidance (#45). @inglesp (and possibly @sebbacon) think there's a need to offer guidance.^1 However, it's not clear what "using Git effectively" means within the context of study code. (I'm reminded of a researcher recently saying something like "I don't know how to use Git. Am I a bad person?")

We should consider:

• formulating some guidelines
• getting some feedback from researchers and software developers
• updating the "How to use Git effectively" page

Note that the Team Manual has a "Git and GitHub etiquette" page, which is directed at members of the tech team.