Document "ends_with" rule (laravel#5183)

This is in conjunction with PR [#28455](laravel/framework#28455) to the framework.

validation.md

@@ -560,6 +560,7 @@ Below is a list of all available validation rules and their function:
 [Dimensions (Image Files)](#rule-dimensions)
 [Distinct](#rule-distinct)
 [E-Mail](#rule-email)
+[Ends With](#rule-ends-with)
 [Exists (Database)](#rule-exists)
 [File](#rule-file)
 [Filled](#rule-filled)
@@ -744,6 +745,11 @@ When working with arrays, the field under validation must not have any duplicate
 
 The field under validation must be formatted as an e-mail address.
 
+<a name="rule-ends-with"></a>
+#### ends_with:_foo_,_bar_,...
+
+The field under validation must end with one of the given values.
+
 <a name="rule-exists"></a>
 #### exists:_table_,_column_