doc update (commands and datatypes)

Change-Id: Ia89a179043491be71d0b2d1fac7a6e41b596c91d

doc/source/protocol/commands.rst

@@ -0,0 +1,22 @@
+Commands
+========
+
+The "done" message should be returned quickly, the time scale should
+be in the order of the time needed for communications. Actions which have
+to wait for physical changes, can be triggered with a command. 
+The information about the success of such an action has to be transferred
+via parameters, namely the status parameter.
+
+A command has at least the following properties:
+
+:description:
+  tell what this command does
+
+:arguments:
+  a list of datatypes for the command arguments (may be empty)
+
+:resulttype:
+  the type of the result (may be null)
+  
+
+