[TASK] Add contribution guide

[DanielSiepmann]

No description provided.

[DanielSiepmann]

New PR as this branch now is within the repository, instead of my fork. It is the up to date version of previously #810

[DanielSiepmann]

@sbuerk you already approved the original PR, but still I mention you as you kickstarted this topic.

[DanielSiepmann]

Also contains info from https://git.typo3.org/qa/internal-organization/-/issues/47

[oliverklee]

One general remark on the style: We should either use full sentences (uppercase first letter, with a period at the end) or bullet-list-style sentences (lowercase first letter, no period at the end), but not the current mix of "uppercase first letter, but no period at the end".

Also, I propose we link the TYPO3 CoC and document that the author of a PR is responsible for rebasing it (if it doesn't get merged quickly).

[DanielSiepmann]

Also, I propose we link the TYPO3 CoC

We already have https://github.com/FriendsOfTYPO3/tea/blob/main/CODE_OF_CONDUCT.md, shouldn't that be enough?

[oliverklee]

We already have https://github.com/FriendsOfTYPO3/tea/blob/main/CODE_OF_CONDUCT.md, shouldn't that be enough?

In theory, people should read both documents. In practice, I think linking from the contribution document to either CODE_OF_CONDUCT.md or the TYPO3 CoC probably helps people notice it.