Add Particle Webhook Plugin (#3477)

plugins/inputs/webhooks/particle/README.md

@@ -0,0 +1,39 @@
+# particle webhooks
+
+
+You should configure your Particle.io's Webhooks to point at the `webhooks` service. To do this go to `(https://console.particle.io/)[https://console.particle.io]` and click `Integrations > New Integration > Webhook`. In the resulting page set `URL` to `http://<my_ip>:1619/particle`, and  under `Advanced Settings` click on `JSON` and add:
+
+```
+{
+    "measurement": "your_measurement_name"
+}
+```
+
+If required, enter your username and password, etc. and then click `Save`
+
+
+
+## Events
+
+Your Particle device should publish an event that contains a JSON in the form of:
+```
+String data = String::format("{ \"tags\" : {
+	    \"tag_name\": \"tag_value\", 
+	    \"other_tag\": \"other_value\"
+    }, 
+	\"values\": {
+	    \"value_name\": %f, 
+		\"other_value\": %f, 
+    }
+    }",  value_value, other_value
+	);
+    Particle.publish("event_name", data, PRIVATE);
+```
+
+Escaping the "" is required in the source file.
+The number of tag values and field values is not restrictied so you can send as many values per webhook call as you'd like.
+
+You will need to enable JSON messages in the Webhooks setup of Particle.io, and make sure to check the "include default data" box as well.
+
+
+See [webhook doc](https://docs.particle.io/reference/webhooks/)