Document new 'DeferrableProvider' interface

See laravel/framework#27067

Author: svenluijten

providers.md

@@ -152,24 +152,18 @@ If your provider is **only** registering bindings in the [service container](/do
 
 Laravel compiles and stores a list of all of the services supplied by deferred service providers, along with the name of its service provider class. Then, only when you attempt to resolve one of these services does Laravel load the service provider.
 
-To defer the loading of a provider, set the `defer` property to `true` and define a `provides` method. The `provides` method should return the service container bindings registered by the provider:
+To defer the loading of a provider, implement the `\Illuminate\Contracts\Support\DeferrableProvider` interface and define a `provides` method. The `provides` method should return the service container bindings registered by the provider:
 
     <?php
 
     namespace App\Providers;
 
     use Riak\Connection;
     use Illuminate\Support\ServiceProvider;
+    use Illuminate\Contracts\Support\DeferrableProvider;
 
-    class RiakServiceProvider extends ServiceProvider
+    class RiakServiceProvider extends ServiceProvider implements DeferrableProvider
     {
-        /**
-         * Indicates if loading of the provider is deferred.
-         *
-         * @var bool
-         */
-        protected $defer = true;
-
         /**
          * Register the service provider.
          *