DOC: add header=None to read_excel docstring (pandas-dev#16689)

Author: fl00r

pandas/io/excel.py

@@ -77,7 +77,7 @@
 header : int, list of ints, default 0
     Row (0-indexed) to use for the column labels of the parsed
     DataFrame. If a list of integers is passed those row positions will
-    be combined into a ``MultiIndex``
+    be combined into a ``MultiIndex``. Use None if there is no header.
 skiprows : list-like
     Rows to skip at the beginning (0-indexed)
 skip_footer : int, default 0