[docs] Move code contribution from GettingStarted.rst to Contributing.rst

[MaskRay]

Summary

For code contribution, GettingStarted.rst duplicates information in Contributing.rst.
The dedicated Contributing.rst is a better place for code contribution, so move
the content there.

Notes:

• D41665 added Contributing.rst
• D110976 mentioned git cherry-pick e3659d43d8911e91739f3b0c5935598bceb859aa workaround

[MaskRay]

minor adjustment

[fhahn]

LGTM, thanks!

[nickdesaulniers]

llvm/docs/Contributing.rst

57–62

Consider adding punctuation to your added point, then making the whole bulleted list consistent.

91–94

Consider adding something to denote we also no longer use the mailing list?

and the llvm-commits mailing list is deprecated?

138–140

I'm a big fan of:

$ git rebase --onto main --root branch-with-change

which will rebase branch-with-change onto main, then checkout branch-with-change.

146

Isn't it necessary to merge branch-with-change into main before pushing main?

i.e. I would do:

$ git checkout main
$ git pull
$ git rebase --onto main --root branch-with-change
$ ninja check-$whatever
$ git checkout main
$ git merge -
$ git pull --rebase
$ git push

I guess you're suggesting pushing from the development branch? I guess that should be fine.

[MaskRay]

address comments

[MaskRay]

Thanks for the suggestion. This is mostly a doc move. The important part is that we agree that the code contribution part from GettingStarted.rst can be moved to Contributing.rst, which I assume we have achieved.
I did not intend to change too much wording and try to keep existing paragraphs. I'll push this shortly as @nickdesaulniers seems to have more planned improvement.

llvm/docs/Contributing.rst

91–94

There are quite a few llvm-commits which may need to be reworded after the Discourse migration.
I just add back a sentence to denote what we used to do.

146

Thanks for the suggestion. This is mostly a doc move from Contributing.rst. The important part is that we agree that the code contribution part from GettingStarted.rst can be moved to Contributing.rst, which I assume we have achieved.