Added a pointer to wiki in readme

README

@@ -1,3 +1,9 @@
+ONLINE DOCUMENTATION
+
+You can find the latest Spark documentation, including a programming guide, on the project wiki at http://github.com/mesos/spark/wiki. This file only contains basic instructions for getting set up.
+
+
+
 BUILDING
 
 Spark requires Scala 2.8. This version has been tested with 2.8.1.final.
@@ -19,6 +25,7 @@ to connect to. This can be a Mesos URL, or "local" to run locally with one
 thread, or "local[N]" to run locally with N threads.
 
 
+
 CONFIGURATION
 
 Spark can be configured through two files: conf/java-opts and conf/spark-env.sh.