bpo-12159: Document sys.maxsize limit in len() function reference (GH-17934)

Doc/library/functions.rst

@@ -892,6 +892,11 @@ are always available.  They are listed here in alphabetical order.
    sequence (such as a string, bytes, tuple, list, or range) or a collection
    (such as a dictionary, set, or frozen set).
 
+   .. impl-detail::
+
+      ``len`` raises :exc:`OverflowError` on lengths larger than
+      :data:`sys.maxsize`, such as :class:`range(2 ** 100) <range>`.
+
 
 .. _func-list:
 .. class:: list([iterable])