Doc about elasticsearch#78276 (#93873)

👋🏼 Regardless of if we decide to validation enforce #78276, may we please drop a doc note that users should avoid duplicating repositories (particularly bucket / base paths).

docs/reference/snapshot-restore/register-repository.asciidoc

@@ -43,6 +43,7 @@ data between repositories.
 +
 --
 // tag::multi-cluster-repo[]
+Clusters should only register a particular snapshot repository bucket once. 
 If you register the same snapshot repository with multiple clusters, only one
 cluster should have write access to the repository. On other clusters, register
 the repository as read-only.