message: readme: show how to use a promise
diff: @@ -62,14 +62,20 @@ var airbrake = new airbrakeJs.Client({projectId: 1, projectKey: 'abc'});
  Or if you are using browserify/webpack/etc:
  ```js
  -var airbrakeJs = require('airbrake-js');
  -var airbrake = new airbrakeJs({projectId: 1, projectKey: 'abc'});
  +var AirbrakeClient = require('airbrake-js');
  +var airbrake = new AirbrakeClient({projectId: 1, projectKey: 'abc'});
  ```
  -You can send a textual message to Airbrake:
  +Then you can send a textual message to Airbrake:
  ```js
  -airbrake.notify(`user id=${user_id} not found`);
  +var promise = airbrake.notify(`user id=${user_id} not found`);
  +promise.then(function(notice) {
  + console.log('notice id', notice.id);
  +});
  +promise.catch(function(err) {
  + console.log('airbrake error', err);
  +});
  ```
  Or report catched errors directly:
  