message: doc: clarify handling of duplicate xDS resource names
  Risk Level: Low
  Testing: N/A
  Docs Changes: Included in PR
  Release Notes: N/A
diff: @@ -449,6 +449,12 @@ no mechanism for providing incremental updates of repeated fields within a named
  Most notably, there is currently no mechanism for incrementally updating individual
  endpoints within an EDS response.
  +Duplicate Resource Names
  +^^^^^^^^^^^^^^^^^^^^^^^^
  +
  +It is an error for a server to send a single response that contains the same resource name
  +twice. Clients should NACK responses that contain multiple instances of the same resource name.
  +
  Deleting Resources
  ^^^^^^^^^^^^^^^^^^
  