upd readme: add description for mqtt connection

README.md

@@ -11,7 +11,7 @@ This repository is a centralized version of architecture for IPos software (Indo
 ## How to run?
 
 1. Start [hivemq](http://www.hivemq.com/demos/websocket-client/). It's a client for an external test MQTT-broker.
-    1. Establish a connection with the standard parameters (WS coonection).
+    1. Establish a connection with the standard parameters (WS connection).
     2. Add new subscriptions with `Add New Topic Subscription` button
         - `test51/subscribe/positions`: responses
         - `test51/publish/positions`: requests
@@ -25,6 +25,24 @@ This repository is a centralized version of architecture for IPos software (Indo
 
 ![](demo.v1.jpg)
 
+## Configurations
+- External MQTT broker
+  - Parameters for a connection are in `src/main/resources/application.yml`  
+    - ```yaml
+        mqtt:
+          automaticReconnect: true
+          cleanSession: true
+          setKeepAliveInterval: 10
+          connectionTimeout: 20
+          clientId: ipos.project
+          hostname: broker.hivemq.com
+          port: 1883
+        ```
+    - Parameters are used in `src/main/java/ipos/project/config/MqttConfig.java`
+      - `@ConfigurationProperties(prefix = "mqtt")` refers to all relevant parameters
+      - create `MqttConnectOptions` bean
+      - create `MqttAsyncClient` bean. Require `MqttConnectOptions`
+
 
 ### Extra
 - Internal database: [localhost:8077/h2-console](http://localhost:8077/h2-console)