Update README.md

Add info about using it with Sentry

Author: Sergio Daniel Xalambrí

Diff for: README.md

@@ -22,3 +22,46 @@ const store = createStore(reducer, applyMiddleware(
 - `reduxCatch` receive a function to use when an error happen.
 - The error handler function could be just a `console.error` like the example above or a function to log the error in some kind of error tracking platform.
 - You should use this middleware as the first middleware in the chain, so its allowed to catch all the possible errors in the application.
+
+### Using it with [Sentry](https://www.getsentry.com/)
+To use it with Sentry just download the Sentry script from npm:
+
+```bash
+npm i -S raven-js raven-node
+```
+- [raven-js](https://www.npmjs.com/package/raven-js): This is the client for browser usage.
+- [raven-node](https://github.com/getsentry/raven-node): This is the client for server usage.
+
+Now load and configure your client:
+
+```javascript
+import Raven from 'raven-js';
+
+const sentryKey = '<key>';
+
+Raven
+  .config(`https://${sentryKey}@app.getsentry.com/<project>`)
+  .install();
+```
+
+And then use `Raven.captureException` as the error handler like this:
+
+```javascript
+const store = createStore(reducer, applyMiddleware(
+  reduxCatch(Raven.captureException)
+));
+```
+
+Now `redux-catch` will start to send the errors of your reducers and middlewares to Sentry.
+
+#### Add state as extra data
+You can also add the state data as extra data for your errors so you can know the state at the moment of the error.
+
+```javascript
+function errorHandler(error, getState) {
+  Raven.context({
+    state: getState(),
+  });
+  Raven.captureException(error);
+}
+```