Add command entity creation documentation

doc/api.md

@@ -9,6 +9,7 @@
         -   [Config groups](#config-groups)
         -   [Devices](#devices)
     -   [Entity attributes](#entity-attributes)
+    -   [Device autoprovision and entity creation](#device-autoprovision-and-entity-creation)
     -   [Multientity support)](#multientity-support)
     -   [Metadata support](#metadata-support)
         -   [NGSI LD data and metadata considerations](#ngsi-ld-data-and-metadata-considerations)
@@ -29,6 +30,7 @@
         -   [Measurement transformation execution](#measurement-transformation-execution)
         -   [Measurement transformation order](#measurement-transformation-order)
         -   [Multientity measurement transformation support (`object_id`)](#multientity-measurement-transformation-support-object_id)
+    -   [Commands execution](#commands-execution)
     -   [Timestamp Processing](#timestamp-processing)
     -   [Overriding global Context Broker host](#overriding-global-context-broker-host)
     -   [Multitenancy, FIWARE Service and FIWARE ServicePath](#multitenancy-fiware-service-and-fiware-servicepath)
@@ -215,6 +217,12 @@ Note that, when information coming from devices, this means measures, are not de
 device, the IoT agent will store that information into the destination entity using the same attribute name than the
 measure name, unless `explicitAttrs` is defined. Measures `id` or `type` names are invalid, and will be ignored.
 
+## Device autoprovision and entity creation
+
+For those agents that uses IoTA Node LIB version 3.4.0 or higher, you should consider that the entity is not created
+automaticaly when a device is created. This means that al entities into the context broker are created when data 
+arrives from a device, either if the device is created or autoprovisioned.
+
 ## Multientity support
 
 The IOTA is able to persists measures coming from a single device to more than one entity, declaring the target entities
@@ -955,6 +963,33 @@ The IOTA processes the entity attributes looking for a `TimeInstant` attribute.
 adds a `TimeInstant` attribute as metadata for every other attribute in the same request. With NGSI-LD, the Standard
 `observedAt` property-of-a-property is used instead.
 
+## Commands execution
+
+The way to act upon devices is through the usage of commnamds. Commands are specific set attributes that allows to 
+send information to the device. They are defined in the device provision.
+
+In order to trigger the command, it is required to update the command attribute in the Orion Context Broker. You 
+can use a PUT request as the following one:
+
+```bash
+curl -L -X PUT 'http://localhost:1026/v2/entities/<ENTITY_ID>/attrs/<CMD_NAME>?type=<ENTITY_TYPE>' \
+-H 'Content-Type: application/json' \
+-d '{
+      "type" : "command",
+      "value" : "commandValue"
+}'
+```
+
+**Note**: It is mandatory to add the `type` URL parameter with the entity type to the request, otherwise, you could 
+get the following error message:
+
+```json
+{
+    "error": "NotFound",
+    "description": "The requested entity has not been found. Check type and id"
+}
+```
+
 ## Overriding global Context Broker host
 
 **cbHost**: Context Broker host URL. This option can be used to override the global CB configuration for specific types