add GemStone installation instructions

README.md

@@ -15,4 +15,16 @@ Grease tries to be concise and consistent. Despite its pragmatic approach, we st
 
 Grease does not try to solve all problems. We are not testing Sockets or HTTP clients. We don’t expect platforms to have standard SSL or graphics libraries. Its scope may grow over time, but for now we’re focusing on extending the functionality of the core classes defined in the ANSI standard (collections, exceptions, streams, blocks, etc.) and on other pieces of functionality that are critical to the Seaside project (e.g. random number generation and secure hashing).
 
-Grease is widely adopted. Implementations exist already for all platforms that support Seaside 3.x. As well as Seaside, new versions of Magritte, Pier, and Monticello are already being implemented on top of Grease. 
+Grease is widely adopted. Implementations exist already for all platforms that support Seaside 3.x. As well as Seaside, new versions of Magritte, Pier, and Monticello are already being implemented on top of Grease.
+
+##GemStone Installation
+
+GsUpgrader works on all versions of GemStone against all Versions of GLASS:
+
+```Smalltalk
+Gofer new
+  package: 'GsUpgrader-Core';
+  url: 'http://ss3.gemtalksystems.com/ss/gsUpgrader';
+  load.
+(Smalltalk at: #GsUpgrader) upgradeGrease.
+```