Document that issues should/may open in root-project/root and PR should be open in root-project/root in general

[SimeonEhrig]

I really often read, that it is better to open a issue in root-project/root. So this should be documented. If it makes sense also disable issues for root-project/cling.

PR's should be disabled in general, because the workflow, first open a PR in root-project/root, merge it and it will be automatically back ported. This needs also be documented. At the moment the PR workflow is insider knowledge.

[gnrv]

I found a bug in cling built from commit ee36b3a (HEAD -> master, tag: __internal-root-9be8b101b7d5e6cb4832afa6c9e24ec2d1347784) but that is not reproducible in the version of root currently in conda (Welcome to ROOT 6.32.02, Built for linuxx8664gcc on Sep 18 2024, 20:01:03 From heads/master@tags/v6-32-02). Would it make sense to report such an issue against cling, or should I report an issue against root despite it perhaps not being reproducible in a released version?