doc: update reference to Features class, add NetVMMixin

doc/qubes-vm/index.rst

@@ -55,7 +55,11 @@ Main public classes
 Helper classes and functions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-.. autoclass:: qubes.vm.Features
+.. autoclass:: qubes.features.Features
+   :members:
+   :show-inheritance:
+
+.. autoclass:: qubes.vm.mix.net.NetVMMixin
    :members:
    :show-inheritance: