Readme cleanup

README.md

@@ -140,6 +140,8 @@ full implementation details.
 
 ### <u>Phase 3 (Open)</u>
 
+The following tags should be considered purely as proposals.  They should not be relied upon or implemented except for testing purposes and experimentation.
+
 - **\<podcast:id platform="[service slug]" id="[platform id]" url="[link to the podcast page on the service]" />**
 
    Channel