update description of custom pivot model capabilities (#7895)

custom pivot models can do more than just define methods, such as cast attributes. we'll also make the wording a little more open ended so the reader doesn't think the capabilities are limited.

Author: browner12

eloquent-relationships.md

@@ -663,7 +663,7 @@ You can also filter the results returned by `belongsToMany` relationship queries
 <a name="defining-custom-intermediate-table-models"></a>
 ### Defining Custom Intermediate Table Models
 
-If you would like to define a custom model to represent the intermediate table of your many-to-many relationship, you may call the `using` method when defining the relationship. Custom pivot models give you the opportunity to define additional methods on the pivot model.
+If you would like to define a custom model to represent the intermediate table of your many-to-many relationship, you may call the `using` method when defining the relationship. Custom pivot models give you the opportunity to define additional behavior on the pivot model, such as methods and casts.
 
 Custom many-to-many pivot models should extend the `Illuminate\Database\Eloquent\Relations\Pivot` class while custom polymorphic many-to-many pivot models should extend the `Illuminate\Database\Eloquent\Relations\MorphPivot` class. For example, we may define a `Role` model which uses a custom `RoleUser` pivot model: