Add HowTo GIT bisect the core within an composer based TYPO3 project

[josefglatz]

Found this really helpful https://forge.typo3.org/issues/91357#note-4 and desided therefore to add a PR for this. Since I'm new to git bisect it will be more initial proposal.

[sypets]

@josefglatz Can you follow up on this? I don't know git bisect and don't know if it will be useful.

[susannemoog]

I think the main point here is to add the composer based git core contribution setup to the contribution guide, because that way we have the best of both worlds (everything is based on composer but we still have access to the core checkout)

[sypets]

Hi @josefglatz You assigned yourself to this issue. Is there any progress here? Would you like to discuss it on Slack or add a PR?

[sypets]

clarification:

This is how we test composer mode when developing on git master.

https://forge.typo3.org/issues/91357#note-4