add more documentation for 'none' channel

Signed-off-by: Dominik Guggemos <dominik.guggemos@bosch-si.com>

documentation/src/main/resources/pages/ditto/protocol-specification-topic.md

@@ -61,6 +61,13 @@ unauthorized access to a `Thing` by responding with an error.
 Protocol messages with the *messages* `{criterion}` are only possible on the *live* channel as Ditto only acts as a
 broker of connected actual devices.
 
+### No channel
+
+Some commands (e.g. Policy commands) are not related to an actual device and thus have no associated twin. 
+For these commands the *twin*/*live* semantics does not fit and consequently they have no channel assigned in the
+ *Topic* of the Ditto Protocol message.
+
+For example a *CreatePolicy* command has the following *Topic*: `<namespace>/<policyName>/policies/commands/create`
 
 ## Criterion
 

documentation/src/main/resources/pages/ditto/protocol-twinlive.md

@@ -25,3 +25,9 @@ specific to the solution and thus out of Ditto's scope.
 
 What Ditto however does, when routing **live** commands/messages, is an [authorization check](basic-auth.html).
 Thus Ditto ensures that only authorized parties are able to send commands or messages.
+
+## Other
+
+Policy commands, do not fit any of the above two categories as they are not directly related to a device. A Policy is 
+not a **twin** of a device. Hence, the **live** channel cannot be used to address the device directly.
+Therefore Policy commands have no *channel* in the Ditto Protocol format specification.