docs: add token part to readme (#26)

update readme

Author: CFenner

README.md

@@ -38,10 +38,15 @@ Add the module configuration to your `config.js` file.
 	header: 'AQI', //choose a header if you like
 	config: {
 	  location: 'beijing' // the location to check the index for
+    token: '' // add your token here
 	}
 },
 ```
 
+### Token
+
+To use the WAQI API you need to [request a token](https://aqicn.org/data-platform/token/).
+
 ### Location
 
 Determine the station you want to display. Select a station on the [map](https://aqicn.org/here/) and copy the location part from the URL. For example http://aqicn.org/city/netherland/utrecht/griftpark/ would be `netherland/utrecht/griftpark/`.

helper.js

@@ -12,7 +12,6 @@ module.exports = {
   },
   start: function () {
     console.log('AirQuality helper started ...')
-    this.token = null
   },
   loadData: async function (config) {
     const self = this