Merge pull request apache#100 from mesosphere/spark-382-document-vers…

…ions

[SPARK-382] Document versions

docs/run-job.md

@@ -12,7 +12,7 @@ more][13].
 
         $ dcos spark run --submit-args=`--class MySampleClass http://external.website/mysparkapp.jar 30`
 
-    
+
         $ dcos spark run --submit-args="--py-files mydependency.py http://external.website/mysparkapp.py 30"
 
     `dcos spark run` is a thin wrapper around the standard Spark
@@ -62,6 +62,20 @@ To set Spark properties with a configuration file, create a
 `spark-defaults.conf` file and set the environment variable
 `SPARK_CONF_DIR` to the containing directory. [Learn more][15].
 
+# Versioning
+
+The DC/OS Spark docker image contains OpenJDK 8 and Python 2.7.6.
+
+DC/OS Spark distributions 1.X are compiled with Scala 2.10.  DC/OS
+Spark distributions 2.X are compiled with Scala 2.11.  Scala is not
+binary compatible across minor verions, so your Spark job must be
+compiled with the same Scala version as your version of DC/OS Spark.
+
+The default DC/OS Spark distribution is compiled against Hadoop 2.6
+libraries.  However, you may choose a different version by following
+the instructions in the "Customize Spark Distribution" section [here](install.md).
+
+
 [13]: http://spark.apache.org/docs/latest/submitting-applications.html
 [14]: http://spark.apache.org/docs/latest/configuration.html#spark-properties
 [15]: http://spark.apache.org/docs/latest/configuration.html#overriding-configuration-directory