update dev guide description

Signed-off-by: SammyOina <sammyoina@gmail.com>

docs/dev-guide.md

@@ -226,22 +226,28 @@ which will do this copying of the binaries.
 Mainflux depends on several infrastructural services, notably the default message broker, [NATS](https://www.nats.io/) and [PostgreSQL](https://www.postgresql.org/) database.
 
 #### Message Broker
+
 Mainflux uses NATS as it's default central message bus. For development purposes (when not run via Docker), it expects that NATS is installed on the local system.
 
 To do this execute:
 
-```
-go get github.com/nats-io/gnatsd
+```bash
+go install github.com/nats-io/nats-server/v2@latest
 ```
 
-This will install `gnatsd` binary that can be simply run by executing:
+This will install `nats-server` binary that can be simply run by executing:
 
-```
-gnatsd
+```bash
+nats-server
 ```
 
-If you want to change the default message broker to [RabbitMQ](https://www.rabbitmq.com/download.html), [VerneMQ](https://vernemq.com/downloads/) or [Kafka](https://kafka.apache.org/quickstart) you need to install it on the local system.
+If you want to change the default message broker to [RabbitMQ](https://www.rabbitmq.com/download.html) or [VerneMQ](https://vernemq.com/downloads/) you need to install it on the local system.
+To run using a different broker you need to set the `MF_BROKER_TYPE` env variable to `nats`, `rabbitmq` or `vernemq` during make and run process.
 
+```bash
+MF_BROKER_TYPE=<broker-type> make
+MF_BROKER_TYPE=<broker-type> make run
+```
 
 #### PostgreSQL
 Mainflux uses PostgreSQL to store metadata (`users`, `things` and `channels` entities alongside with authorization tokens).

docs/edge.md

@@ -534,7 +534,7 @@ git clone https://github.com/mainflux/agent
 go run ./examples/publish/main.go -s http://localhost:4222 export.test "[{\"bn\":\"test\"}]";
 ```
 
-We have configured route for export, `nats_topic = ">"` means that it will listen to `NATS` subject `export.>` and `mqtt_topic` is configured so that data will be sent to MQTT broker on topic `channels/e2adcfa6-96b2-425d-8cd4-ff8cb9c056ce/messages` with appended `NATS` subject. Depending on the broker used, nats by default, rabbitmq can be used by setting the build tag to `rabbitmq`.
+We have configured route for export, `nats_topic = ">"` means that it will listen to `NATS` subject `export.>` and `mqtt_topic` is configured so that data will be sent to MQTT broker on topic `channels/e2adcfa6-96b2-425d-8cd4-ff8cb9c056ce/messages` with appended `NATS` subject. Other brokers can such as `rabbitmq` can be used, for more detail refer to [dev-guide][dev-guide].
 
 In terminal where export is started you should see following message:
 
@@ -553,3 +553,4 @@ mainflux-mqtt   | {"level":"info","message":"Publish - client ID export-88529fb2
 [env]:(https://github.com/mainflux/export#environmet-variables)
 [agent]:(https://github.com/mainflux/agent)
 [protomsg]:https://github.com/mainflux/mainflux/blob/master/pkg/messaging/message.proto
+[dev-guide]: /docs/dev-guide.md/#message-broker