DOC: Add documentation for delim_whitespace

Addresses DOC issue part of pandas-devgh-12912.

Author: gfyoung

doc/source/io.rst

@@ -97,6 +97,12 @@ sep : str, defaults to ``','`` for :func:`read_csv`, ``\t`` for :func:`read_tabl
   Regex example: ``'\\r\\t'``.
 delimiter : str, default ``None``
   Alternative argument name for sep.
+delim_whitespace : boolean, default False
+  Specifies whether or not whitespace (e.g. ``' '`` or ``'\t'``)
+  will be used as the delimiter. Equivalent to setting ``sep='\+s'``.
+  If this option is set to True, nothing should be passed in for the
+  ``delimiter`` parameter. This parameter is currently supported for
+  the C parser only.
 
 Column and Index Locations and Names
 ++++++++++++++++++++++++++++++++++++

pandas/io/parsers.py

@@ -209,6 +209,11 @@
 warn_bad_lines : boolean, default True
     If error_bad_lines is False, and warn_bad_lines is True, a warning for each
     "bad line" will be output. (Only valid with C parser).
+delim_whitespace : boolean, default False
+    Specifies whether or not whitespace (e.g. ``' '`` or ``'\t'``) will be used
+    as the delimiter. Equivalent to setting ``sep='\+s'``. If this option is set
+    to True, nothing should be passed in for the ``delimiter`` parameter. This
+    parameter is currently supported for the C parser only.
 
 Returns
 -------