[SPARK-27261][DOC] Improve app submission doc for passing multiple configs

## What changes were proposed in this pull request?

While submitting the spark application, passing multiple configurations not documented clearly, no examples given.it will be better if it can be documented since  clarity is less from spark documentation side.
Even when i was browsing i could see few queries raised by users, below provided the reference.

https://community.hortonworks.com/questions/105022/spark-submit-multiple-configurations.html

 As part of fixing i had documented the above scenario  with an example.

## How was this patch tested?
Manual inspection of the updated document.

Closes apache#24191 from sujith71955/master_conf.

Authored-by: s71955 <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: sujith71955

docs/submitting-applications.md

@@ -44,7 +44,7 @@ Some of the commonly used options are:
 * `--class`: The entry point for your application (e.g. `org.apache.spark.examples.SparkPi`)
 * `--master`: The [master URL](#master-urls) for the cluster (e.g. `spark://23.195.26.187:7077`)
 * `--deploy-mode`: Whether to deploy your driver on the worker nodes (`cluster`) or locally as an external client (`client`) (default: `client`) <b> &#8224; </b>
-* `--conf`: Arbitrary Spark configuration property in key=value format. For values that contain spaces wrap "key=value" in quotes (as shown).
+* `--conf`: Arbitrary Spark configuration property in key=value format. For values that contain spaces wrap "key=value" in quotes (as shown). Multiple configurations should be passed as separate arguments. (e.g. `--conf <key>=<value> --conf <key2>=<value2>`)
 * `application-jar`: Path to a bundled jar including your application and all dependencies. The URL must be globally visible inside of your cluster, for instance, an `hdfs://` path or a `file://` path that is present on all nodes.
 * `application-arguments`: Arguments passed to the main method of your main class, if any