[SPARK-595][DOCS] Add local-cluster mode option in Documentation

### What changes were proposed in this pull request?

Add local-cluster mode option to submitting-applications.md

### Why are the changes needed?

Help users to find/use this option for unit tests.

### Does this PR introduce _any_ user-facing change?

Yes, docs changed.

### How was this patch tested?

`SKIP_API=1 bundle exec jekyll build`
<img width="460" alt="docchange" src="https://user-images.githubusercontent.com/87687356/127125380-6beb4601-7cf4-4876-b2c6-459454ce2a02.png">

Closes #33537 from yutoacts/SPARK-595.

Lead-authored-by: Yuto Akutsu <[email protected]>
Co-authored-by: Yuto Akutsu <[email protected]>
Co-authored-by: Yuto Akutsu <[email protected]>
Signed-off-by: Thomas Graves <[email protected]>

Author: 3 people

docs/submitting-applications.md

@@ -162,9 +162,10 @@ The master URL passed to Spark can be in one of the following formats:
 <tr><th>Master URL</th><th>Meaning</th></tr>
 <tr><td> <code>local</code> </td><td> Run Spark locally with one worker thread (i.e. no parallelism at all). </td></tr>
 <tr><td> <code>local[K]</code> </td><td> Run Spark locally with K worker threads (ideally, set this to the number of cores on your machine). </td></tr>
-<tr><td> <code>local[K,F]</code> </td><td> Run Spark locally with K worker threads and F maxFailures (see <a href="configuration.html#scheduling">spark.task.maxFailures</a> for an explanation of this variable) </td></tr>
+<tr><td> <code>local[K,F]</code> </td><td> Run Spark locally with K worker threads and F maxFailures (see <a href="configuration.html#scheduling">spark.task.maxFailures</a> for an explanation of this variable). </td></tr>
 <tr><td> <code>local[*]</code> </td><td> Run Spark locally with as many worker threads as logical cores on your machine.</td></tr>
 <tr><td> <code>local[*,F]</code> </td><td> Run Spark locally with as many worker threads as logical cores on your machine and F maxFailures.</td></tr>
+<tr><td> <code>local-cluster[N,C,M]</code> </td><td> Local-cluster mode is only for unit tests. It emulates a distributed cluster in a single JVM with N number of workers, C cores per worker and M MiB of memory per worker.</td></tr>
 <tr><td> <code>spark://HOST:PORT</code> </td><td> Connect to the given <a href="spark-standalone.html">Spark standalone
         cluster</a> master. The port must be whichever one your master is configured to use, which is 7077 by default.
 </td></tr>