Fix yarn/README.md

yarn/README.md

 # YARN DIRECTORY LAYOUT
 
-Hadoop Yarn related codes are organized in separate modules with layered dependency.
+Hadoop Yarn related codes are organized in separate directories for easy management.
 
- * common : Common codes that will be called into by other modules.
+ * common : Common codes that do not depending on specific version of Hadoop.
 
- * 2.0 / 2.2 : Codes that involve specific version of Hadoop YARN API. Depends on common module.
+ * 2.0 / 2.2 : Codes that involve specific version of Hadoop YARN API.
 
   2.0 actually represents  0.23 and 2.0
   2.2 actually represents 2.2 and later, until the API is break again.
 
- * Scheduler : Implementation of various YARN Scheduler and backend. Depends on 2.0 / 2.2 modules.
- * Assembly : For maven build to assembly all other modules in Yarn into one single jar.
-
+2.0 / 2.2 will build together with common dir into a single jar