Add compatibility note

diff --git a/README b/README
index 71537fb..7805b95 100644
--- a/README
+++ b/README
@@ -23,6 +23,10 @@ This script :
   - check if stand-by client(s) is connected (WARNING raise if not)
   - Return OK state with list and count of stand-by client(s)

+Note : This script was originally write and test for PostgreSQL 9.1, but it could be compatible
+with other versions of PostgreSQL. Do not hesitate to tell me how this script work with other
+versions and share some fix. All contributions are welcome !
+
 Requirements
 ------------