[Docs]: Add some more documentation on how to work with github.

[PhilipMetzger]

The document roughly describes some workflows, which help new users to start with github.

@superpippo12 Discord self ping.

Rendered

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have added tests to cover my changes

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[PhilipMetzger]

There are only a few things missing from this doc, but generally it's ready.

[martinvonz]

There are only a few things missing from this doc, but generally it's ready.

Okay, I'll click the "Ready for review" button :)

[PhilipMetzger]

i'll need to tidy up the revsets section and then it's ready. If you see sentences which I could structure better, I'll gladly change them.

[PhilipMetzger]

Since the last Revision, I removed both the Git and Mercurial sections and introduced @martinvonz suggestion as basic workflow. PTAL at both the revsets and the basic workflow section. Overall the doc was vastly simplified.

[martinvonz]

I still have a lot of comments, but I think this is a good start. Thanks! Feel free to merge this as is, and then I'll probably go over it and send a follow-up PR later instead.