Add redaction info to main readme

Author: stefpiatek

README.md

@@ -1,5 +1,10 @@
 # **OMOP Extraction System**
 
+> [!WARNING] 
+> This repository is a one-off artifact for public inspection only. All electronic health record intellectual property has been removed to allow for public release. It is expected that the tests and code here will **not function** as-is.  
+> For access to the unredacted full pipeline, please contact [uclh.safehr@nhs.net](mailto:uclh.safehr@nhs.net).  
+> We plan to release a scalable, open-source framework in the future.
+
 # Introduction and Goals
 
 omop_es has been developed to provide OMOP extracts of NHS data to