chore: add note explaining google-api-core, google-cloud-core < 3.0.0dev pin (#400)
chore: add note explaining google-api-core, google-cloud-core < 3.0.0dev pin (#400)

Expand pins on library dependencies in preparation for these dependencies taking a new major version. See https://github.com/googleapis/google-cloud-python/issues/10566.
googleapis/python-firestore,googleapis/python-firestore