* New entries in glossary.md
* Clarify repo names in labels.md
* Docs for REPO.bazel, `use_repo_rule`

Fixes https://github.com/bazelbuild/bazel/issues/15821.

PiperOrigin-RevId: 590246296
Change-Id: Idba4c35fdb068f9befba1122e3724880ba8fd1c8