DOC: New storage_options for read_csv needs a docstring
#### Location of the documentation

https://pandas.pydata.org/docs/dev/reference/api/pandas.read_csv.html
#### Documentation problem

The new `storage_options` keyword for `read_csv` and `read_table` is not documented in the docstring.  

#### Suggested fix for documentation

Add docstring

@martindurant 

NOTE:  I noticed this when running `validate_docstrings` locally for `read_csv` and it reported this.
