[SPARK-4652][DOCS] Add docs about spark-git-repo option

There might be some cases when WIPS spark version need to be run
on EC2 cluster. In order to setup this type of cluster more easily,
add --spark-git-repo option description to ec2 documentation.

Author: lewuathe <lewuathe@me.com>
Author: Josh Rosen <joshrosen@databricks.com>

Closes #3513 from Lewuathe/doc-for-development-spark-cluster and squashes the following commits:

6dae8ee [lewuathe] Wrap consistent with other descriptions
cfaf9be [lewuathe] Add docs about spark-git-repo option

(Editing / cleanup by Josh Rosen)

(cherry picked from commit ab8177da2defab1ecd8bc0cd5a21f07be5b8d2c5)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>
[SPARK-4421] Wrong link in spark-standalone.html

Modified the link of building Spark. (backport version of #3279.)

Author: Masayoshi TSUZUKI <tsudukim@oss.nttdata.co.jp>

Closes #3280 from tsudukim/feature/SPARK-4421-2 and squashes the following commits:

3b4d38d [Masayoshi TSUZUKI] [SPARK-4421] Wrong link in spark-standalone.html
Fix typo in Spark SQL docs.

Author: Andy Konwinski <andykonwinski@gmail.com>

Closes #3611 from andyk/patch-3 and squashes the following commits:

7bab333 [Andy Konwinski] Fix typo in Spark SQL docs.

(cherry picked from commit 15cf3b0125fe238dea2ce13e703034ba7cef477f)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>