Update readme with conditional service provider registration

Author: jenssegers

README.md

@@ -17,6 +17,14 @@ Install using composer:
 Add the service provider to the `'providers'` array in `config/app.php`:
 
     Jenssegers\Rollbar\RollbarServiceProvider::class,
+    
+If you only want to enable Rollbar reporting for certain environments you can conditionally load the service provider in your `AppServiceProvider`:
+
+```php
+if ($this->app->environment('production')) {
+    $this->app->register(Jenssegers\Rollbar\RollbarServiceProvider::class);
+}
+```
 
 Configuration
 -------------