Adding hybrid relations to the readme

Author: jenssegers

README.md

@@ -350,6 +350,40 @@ The belongsToMany relation will not use a pivot "table", but will push id's to a
 
 Other relations are not yet supported, but may be added in the future. Read more about these relations on http://four.laravel.com/docs/eloquent#relationships
 
+### MySQL Relations
+
+If you're using a hybrid MongoDB and SQL setup, you're in luck! The model will automatically return a MongoDB- or SQL-relation based on the type of the related model. Of course, if you want this functionality to work both ways, your SQL-models will need to extend `Jenssegers\Eloquent\Model`. Note that this functionality only works for hasOne, hasMany and belongsTo relations.
+
+Example SQL-based User model:
+
+    use Jenssegers\Eloquent\Model as Eloquent;
+
+    class User extends Eloquent {
+
+        protected $connection = 'mysql';
+
+        public function messages()
+        {
+            return $this->hasMany('Message');
+        }
+
+    }
+
+And the Mongodb-based Message model:
+
+    use Jenssegers\Mongodb\Model as Eloquent;
+
+    class Message extends Eloquent {
+
+        protected $connection = 'mongodb';
+
+        public function user()
+        {
+            return $this->belongsTo('User');
+        }
+
+    }
+
 ### Raw Expressions
 
 These expressions will be injected directly into the query.