package/python-typing-extensions: update homepage link in help

Typing-extensions has moved to a separate repository, the previous
link now leads to a 404 page. The top level README in the previous
repository points at the new one, see:
https://github.com/python/typing/blob/fafcdeb724ac22ace877bee4485ed3b4c3edbbd8/README.md#repository-content

Signed-off-by: Fiona Klute (WIWA) <fiona.klute@gmx.de>
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit a40ea829ab45d56434d0b53016a8c51f4c98d04a)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/python-typing-extensions/Config.in

@@ -3,4 +3,4 @@ config BR2_PACKAGE_PYTHON_TYPING_EXTENSIONS
 	help
 	  Backported and Experimental Type Hints for Python 3.5+.
 
-	  https://github.com/python/typing/blob/master/typing_extensions/README.rst
+	  https://github.com/python/typing_extensions