Docs(readme): Updated documentation

README.md

@@ -17,35 +17,31 @@ Unofficial Node.js module for the Maxmind GeoIP2 Web Services.
 Usage
 -----
 
-There are multiple ways to load and set up this module.
-All communication is done over HTTPS.
+There are multiple ways to load and use this module.
 
-#### One line
+When you don't provide a callback function you'll get
+a _promise_ in return.
 
-```js
-require ('geoip2ws') (userId, licenseKey) (ip, callback);
-```
 
-#### Multiple calls, same account
+#### One line with callback
 
 ```js
-const geoip2ws = require ('geoip2ws') (userId, licenseKey);
-geoip2ws (ip1, callback);
-geoip2ws (ip2, callback);
+require ('geoip2ws') (userId, licenseKey) (ip, callback);
 ```
 
-#### Mix products (or accounts)
 
-```js
-const geoip2ws = require ('geoip2ws');
-const insights = new geoip2ws (userId, licenseKey, 'insights');
-const country = new geoip2ws (userId, licenseKey, 'country');
+#### Promise
 
-// precise lookup, higher cost
-insights (ip, callback);
+```js
+const geo = require ('geoip2ws') ({
+  userId: 12345,
+  licenseKey: 'abc678',
+});
 
-// vague lookup, lower cost
-country (ip, callback);
+geo ('city', '1.2.3.4')
+  .then (console.log)
+  .catch (console.error)
+;
 ```
 
 
@@ -91,30 +87,12 @@ parameter | type     | required | description
 :---------|:---------|:---------|:--------------------------------------------
 service   | string   | no       | The service, same as above
 ip        | string   | yes      | The IPv4 or IPv6 address to lookup
-callback  | function | yes      | Your callback `function` to receive the data
+callback  | function | no       | Your callback. Leave out to return a promise.
 
 ```js
 geo ('city', '145.53.252.135', myCallback);
 ```
 
-
-Callback
---------
-
-The callback function receives result data and errors. Unless an error occurs the
-data JSON will be parsed to an object. When everything is ok `err` is `null` else
-`err` is an instance of `Error`. It also returns API errors this same way.
-
-```js
-function myCallback (err, data) {
-  if (err) {
-    console.log (err);
-  } else {
-    console.log (data.city.names.en);
-  }
-}
-```
-
 [Example response data](http://dev.maxmind.com/geoip/geoip2/web-services/#Response_Body)
 
 
@@ -165,5 +143,3 @@ Author
 ------
 
 [Franklin van de Meent](https://frankl.in/)
-
-[![Buy me a coffee](https://frankl.in/u/kofi/kofi-readme.svg)](https://ko-fi.com/franklin)