[mqtt.generic] Documentation, postCommand (openhab#4908)

Wasn't clear that the option accepts a boolean value.

Signed-off-by: davidgraeff <[email protected]>
Signed-off-by: Maximilian Hess <[email protected]>

addons/binding/org.openhab.binding.mqtt.generic/README.md

@@ -70,9 +70,11 @@ All things require a configured broker.
 * __transformationPatternOut__: An optional transformation pattern like [JSONPath](http://goessner.net/articles/JsonPath/index.html#e2) that is applied before publishing a value to MQTT.
 * __commandTopic__: The MQTT topic that commands are send to. This can be empty, the thing channel will be read-only then. Transformations are not applied for sending data.
 * __formatBeforePublish__: Format a value before it is published to the MQTT broker. The default is to just pass the channel/item state. If you want to apply a prefix, say "MYCOLOR,", you would use "MYCOLOR,%s". If you want to adjust the precision of a number to for example 4 digits, you would use "%.4f".
-* __postCommand__: If the received MQTT value should not only update the state of linked items, but command them, enable this option. You usually need this enabled if your item is also linked to another channel, say a KNX actor, and you want a received MQTT payload to command that KNX actor. 
+* __postCommand__: If `true`, the received MQTT value will not only update the state of linked items, but command it.
+  The default is `false`.
+  You usually need this to be `true` if your item is also linked to another channel, say a KNX actor, and you want a received MQTT payload to command that KNX actor. 
 * __retained__: The value will be published to the command topic as retained message. A retained value stays on the broker and can even be seen by MQTT clients that are subscribing at a later point in time. 
-* __trigger__: If true, the state topic will not update a state, but trigger a channel instead.
+* __trigger__: If `true`, the state topic will not update a state, but trigger a channel instead.
 
 ### Channel Type "string"