[llvm] [GitHub][workflows] Add buildbot information comment to first merged PR from a new contributor (PR #78292)

[David Spickett via llvm-commits]

DavidSpickett wrote:

@asb I've updated the text to link to https://llvm.org/docs/MyFirstTypoFix.html#myfirsttypofix-issues-after-landing-your-pr, but there's still a considerable overlap as you suggested.

My intent is that the text in the comment warns you about the initial messages you might get, then tells you, if you need to follow up on them, here's the link to a description of all that.

https://github.com/llvm/llvm-project/pull/78292