Update main class name in README

Author: russelldb

README.org

@@ -10,7 +10,7 @@ You need Java and maven.
 #+BEGIN_SRC java
   git clone git://github.com/russelldb/bench_shim.git
   mvn clean install
-  mvn exec:java -Dexec.mainClass="com.basho.riak.bench.BenchDriverApp" -Dexec.classpathScope=runtime -Dexec.args="[email protected] MY_COOKIE"
+  mvn exec:java -Dexec.mainClass="com.basho.riak.bench.BenchShimApp" -Dexec.classpathScope=runtime -Dexec.args="[email protected] MY_COOKIE"
 #+END_SRC
 
 This will start a local Jinterface node. You then need to configure your basho_bench installation to talk to this Java node.