## What changes were proposed in this pull request?
This pr is to add doc for turning off quotations because this behavior is different from `com.databricks.spark.csv`.

## How was this patch tested?
Check behavior  to put an empty string in csv options.

Author: Takeshi YAMAMURO <linguin.m.s@gmail.com>

Closes #13616 from maropu/SPARK-15585-2.