Add highest verification level.

docs/api.rst

@@ -679,6 +679,13 @@ All enumerations are subclasses of `enum`_.
     .. attribute:: table_flip
 
         An alias for :attr:`high`.
+    .. attribute:: highest
+
+        Member must have a verified phone on their Discord account.
+
+    .. attribute:: double_table_flip
+
+        An alias for :attr:`highest`.
 
 .. class:: ContentFilter