Fix introductory sentence.

Doc/library/getopt.rst

@@ -11,7 +11,7 @@ This module helps scripts to parse the command line arguments in ``sys.argv``.
 It supports the same conventions as the Unix :cfunc:`getopt` function (including
 the special meanings of arguments of the form '``-``' and '``--``').  Long
 options similar to those supported by GNU software may be used as well via an
-optional third argument. This module provides a single function and an
+optional third argument. This module provides two functions and an
 exception: