reword

Author: WangTaoTheTonic

docs/running-on-yarn.md

@@ -200,8 +200,8 @@ Most of the configs are the same for Spark on YARN as for other deployment modes
   <td><code>spark.yarn.submit.waitAppCompletion</code></td>
   <td>true</td>
   <td>
-  Whether to wait for application to complete in cluster mode. If set this to true, client process will enter a loop to track application's status.
-  Otherwise, client process will exist as long as application is successfully submitted.
+  In YARN cluster mode, controls whether the client waits to exit until the application completes. If set to true, the client process will stay alive reporting the application's status.
+  Otherwise, the client process will exit after submission.
   </td>
 </tr>
 </table>