Update readme for 1.2.2 release

Author: kbrandl

README.md

@@ -37,6 +37,9 @@ This API documentation is based upon [Slate](https://github.com/tripit/slate/) a
 
 ## Release Notes
 
+**1.2.2 (Sept 21, 2015)**
+* Add new error code (4004); miscellaneous minor doc updates (for clarity).
+
 **1.2.1 (Aug 25, 2015)**
 * Added sample code (C# and Java) for [new endpoints](https://www.smartsheet.com/blog/august-2015-api-update).
 
@@ -47,4 +50,4 @@ This API documentation is based upon [Slate](https://github.com/tripit/slate/) a
 * Added sample code in C#, Java, and Node.js.
 
 **1.0.0 (July 11, 2015)**
-* Initial Release of the Smartsheet API 2.0 Documentation ([more info](https://www.smartsheet.com/blog/july-2015-api-v2-launch))
+* Initial Release of the Smartsheet API 2.0 Documentation ([more info](https://www.smartsheet.com/blog/july-2015-api-v2-launch))