Make TODO file refer to contribute.html web page

We can't just remove it as autohate wants it, but we can at least stop
having horridly out-of-date content in it.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

TODO

@@ -1,7 +1,2 @@
-
-openconnect:
-	Port to/test on Windows, Symbian, etc.
-
-nm-auth-dialog:
-	Store cookie in GNOME keyring and reuse it instead of logging in again
-	      (which means you keep your IP address)
+See the contribute.html web page in the documentation, generated in www/
+or at http://www.infradead.org/openconnect/contribute.html