Mention discussions forum (#5901)

Author: srittau

README.md

@@ -56,6 +56,9 @@ tracker](https://github.com/python/typeshed/issues).  This is the right
 place to start a discussion of any of the above or most any other
 topic concerning the project.
 
+If you have general questions about typing with Python, or you need
+a review of your type annotations or stubs outside of typeshed, head over to
+[our discussion forum](/python/typing/discussions).
 For less formal discussion, try the typing chat room on
 [gitter.im](https://gitter.im/python/typing).  Some typeshed maintainers
 are almost always present; feel free to find us there and we're happy