Add comment to README that 2.10 not yet supported

README.md

@@ -12,12 +12,15 @@ This README file only contains basic setup instructions.
 
 ## Building
 
-Spark requires Scala 2.9.2. The project is built using Simple Build Tool (SBT),
-which is packaged with it. To build Spark and its example programs, run:
+Spark requires Scala 2.9.2 (Scala 2.10 is not yet supported). The project is
+built using Simple Build Tool (SBT), which is packaged with it. To build
+Spark and its example programs, run:
 
     sbt/sbt package
 
-Spark also supports building using Maven. If you would like to build using Maven, see the [instructions for building Spark with Maven](http://spark-project.org/docs/latest/building-with-maven.html) in the spark documentation..
+Spark also supports building using Maven. If you would like to build using Maven,
+see the [instructions for building Spark with Maven](http://spark-project.org/docs/latest/building-with-maven.html)
+in the spark documentation..
 
 To run Spark, you will need to have Scala's bin directory in your `PATH`, or
 you will need to set the `SCALA_HOME` environment variable to point to where