README: Add link to LICENSE (GH-21565)

Thanks @wbnns for your contribution.
diff --git a/README.rst b/README.rst
index 9a646a2..14f4f32 100644
--- a/README.rst
+++ b/README.rst
@@ -259,8 +259,9 @@
 
 Copyright (c) 1991-1995 Stichting Mathematisch Centrum.  All rights reserved.
 
-See the file "LICENSE" for information on the history of this software, terms &
-conditions for usage, and a DISCLAIMER OF ALL WARRANTIES.
+See the `LICENSE <https://github.com/python/cpython/blob/master/LICENSE>`_ for
+information on the history of this software, terms & conditions for usage, and a
+DISCLAIMER OF ALL WARRANTIES.
 
 This Python distribution contains *no* GNU General Public License (GPL) code,
 so it may be used in proprietary projects.  There are interfaces to some GNU