added nodered json example

HOWTO.md

@@ -108,7 +108,22 @@ Change monitors config.
                 scale: 2
               ```
 
-
+            - **Example for Node-RED(JSON):**
+              ```json
+              // Example of the data expression of a service call node in Node-RED.
+              {
+                "monitors_config": {
+                  "HDMI-1": {
+                    "enabled": true,
+                    "primary": true,
+                    "position": [0, 0],
+                    "mode": "3840x2160@120.000",
+                    "transform": "normal",
+                    "scale": 2
+                  }
+                }
+              }
+              ```
 
 ## `steam_big_picture`