message: feat: accept airbrake instance
diff: @@ -7,16 +7,19 @@ npm install airbrake-js redux-airbrake --save
  #### 2. Import dependency
  ``` js
  +import AirbrakeClient from 'airbrake-js';
  import airbrakeMiddleware from 'redux-airbrake';
  ```
  #### 3. Configure & add middleware
  ``` js
  -const errorMiddleware = airbrakeMiddleware({
  +const airbrake = new AirbrakeClient({
  projectId: '******',
  projectKey: '**************'
  });
  +const errorMiddleware = airbrakeMiddleware(airbrake);
  +
  export const store = createStore(
  rootReducer,
  applyMiddleware(
  @@ -27,15 +30,21 @@ export const store = createStore(
  export default store;
  ```
  -#### Adding notice metadata (optional)
  +#### Adding notice annotations (optional)
  +
  +It's possible to annotate error notices with all sorts of useful information at the time they're captured by supplying it in the object being reported.
  ``` js
  -const errorMiddleware = airbrakeMiddleware({
  - projectId: '******',
  - projectKey: '**************'
  -}, {
  +const errorMiddleware = airbrakeMiddleware(airbrake, {
  context: { environment: window.ENV }
  });
  ```
  -[redux-airbrake](https://github.com/alexcastillo/redux-airbrake) on GitHub.
  \ No newline at end of file
  +#### Adding filters
  +
  +Since an Airbrake instrace is passed to the middleware, you can simply add
  +filters to the instance as described here:
  +
  +[https://github.com/airbrake/airbrake-js#filtering-errors](https://github.com/airbrake/airbrake-js#filtering-errors)
  +
  +For more info, visit [redux-airbrake](https://github.com/alexcastillo/redux-airbrake) on GitHub.
  