document that Mesos cluster mode supports python

update docs to be consistent with SPARK-14645 https://issues.apache.org/jira/browse/SPARK-14645

Author: Michael Gummelt <mgummelt@mesosphere.io>

Closes #14514 from mgummelt/fix-docs.

docs/submitting-applications.md

@@ -58,7 +58,8 @@ for applications that involve the REPL (e.g. Spark shell).
 
 Alternatively, if your application is submitted from a machine far from the worker machines (e.g.
 locally on your laptop), it is common to use `cluster` mode to minimize network latency between
-the drivers and the executors. Currently only YARN supports cluster mode for Python applications.
+the drivers and the executors. Currently, standalone mode does not support cluster mode for Python
+applications.
 
 For Python applications, simply pass a `.py` file in the place of `<application-jar>` instead of a JAR,
 and add Python `.zip`, `.egg` or `.py` files to the search path with `--py-files`.