Update readme with notes on bugfix

Author: clairblacketer

README.md

@@ -1,9 +1,13 @@
-Common Data Model v5.1.0
+Common Data Model v5.1.1
 =================
 
 See full CDM specification file on our github [wiki](https://github.com/OHDSI/CommonDataModel/wiki) or in the [CDM V5.1.0 PDF](https://github.com/OHDSI/CommonDataModel/blob/master/OMOP_CDM_v5_1_0.pdf)
 
-Release Notes
+Release Notes for v5.1.1
+=============
+This version has a small bug-fix for impala to make it compatible with ATLAS cohort generation.
+
+Release Notes for v5.1.0
 =============
 This version is based on the CDM working group proposal [#60](https://github.com/OHDSI/CommonDataModel/issues/60) and [#59](https://github.com/OHDSI/CommonDataModel/issues/59) and is **backwards compatibile with v5.0.1**. The proposed and accepted changes include adding a datetime field to every table that had a date column and adding field DENOMINATOR_VALUE to the DRUG_STRENGTH table. These were the new columns added: