Docs/contrib updates

[brenthuisman]

• Add documentation for collaboration on a PR using just git
• Add the stage of Issue creation to PR workflow.
• Correct header level in test docs

[thorstenhater]

Some stylistic issues and typos plus a few suggestions on clarity.

[thorstenhater]

Issue -> issue

[brenthuisman]

Although a bit subtle, I capitalize when I'm referring to things in GH UI. You might have many issues, but until they are Issues, I probably don't know about them.

[thorstenhater]

I like the idea, but maybe highlight in a more obvious way then and explain it. Like written, it seems like a typo.

[brenthuisman]

See below.

[thorstenhater]

Now that we have explained that: replace Isssue with request here

[brenthuisman]

Again, maybe to subtly worded right now, but I want to stress that the thing being addressed exists as a Github Issue. Referring to them as requests is a layer of indirection that I would rather leave out, unless you have a strong argument for doing that anyway.

[thorstenhater]

The sentence as stated

Having an Issue before an implementation addressing the Issue

is syntactically dubious -- at least. Without having an Issue one cannot address it.
Either the first or second Issue should refer to something different. I think you
mean this

Make a (formal GH-kind) Issue before addressing your (desire-for-change-kind) issue (in code/text).

[brenthuisman]

I've updated with a definition (like there already was for PR) the first time the term is used.

[thorstenhater]

I'll accept despite informalisms. They might justified here due to the less formal tone of the section.