update of docstring

Author: charlesdong1991

pandas/core/reshape/merge.py

@@ -161,7 +161,8 @@ def merge_ordered(left, right, on=None,
         Interpolation method for data
     suffixes : 2-length sequence (tuple, list, ...)
         Suffix to apply to overlapping column names in the left and right
-        side, respectively
+        side, respectively. Except for tuple of (str, str), it also allows
+        tuple of (None, str) or (str, None)
     how : {'left', 'right', 'outer', 'inner'}, default 'outer'
         * left: use only keys from left frame (SQL: left outer join)
         * right: use only keys from right frame (SQL: right outer join)
@@ -488,9 +489,7 @@ def __init__(self, left, right, how='inner', on=None,
         self.right_on = com.maybe_make_list(right_on)
 
         self.copy = copy
-
         self.suffixes = suffixes
-
         self.sort = sort
 
         self.left_index = left_index