docs/api: document strict_aud on decode_complete (#923)

Author: woodruffw

docs/api.rst

@@ -106,6 +106,7 @@ API Reference
         * ``verify_exp=verify_signature`` check that ``exp`` (expiration) claim value is in the future
         * ``verify_iat=verify_signature`` check that ``iat`` (issued at) claim value is an integer
         * ``verify_nbf=verify_signature`` check that ``nbf`` (not before) claim value is in the past
+        * ``strict_aud=False`` check that the ``aud`` claim is a single value (not a list), and matches ``audience`` exactly
 
         .. warning::