Update readme.md

Author: smpetersgithub

BabelfishCompass/readme.md

@@ -3,3 +3,5 @@
 [Deep dive into Babelfish Compass (Instructions)](https://aws.amazon.com/blogs/database/deep-dive-into-babelfish-compass/)    
 
 [Babelfish Compass v.2023-12-a (GitHub Install)](https://github.com/babelfish-for-postgresql/babelfish_compass/releases/tag/v.2023-12-a)    
+
+[Unsupported functionality in Babelfish] (https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/babelfish-compatibility.tsql.limitations-unsupported.html)