Improve documentation.

README

@@ -19,6 +19,12 @@ videohubctrl currently displays and can configure:
 Configuration of Videohub's network settings can be made using
 Blackmagic's Windows program when the device is connected via USB.
 
+Confiration of processing units and frames is probably not working
+properly because the support was added by just following the very
+minimal documentation and with no testing on a real device, so don't
+expect miracles in this department. The other stuff is solid but
+please see the TODO section of this document and help.
+
 
 License
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