Add some areas to fill out

README.md

@@ -2,3 +2,10 @@ JRuby Examples
 ==============
 
 This repository contains examples and documentation for features specific to JRuby, like Java integration and Java-based extensions.
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+This repository is divided into a few areas:
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+* java-integration/ contains Ruby-based examples of calling Java from Ruby
+* extensions/ contains examples of JRuby extensions written in Java (and other languages)
+* integration/ holds example projects and builds for various types of applications, like WAR files, standalone jar files, etc.
+* performance/ contains examples of how to get the best performance out of JRuby