docs($cookiesProvider): add example for overwriting defaults on provider

Add an example on how to set default values on `$cookiesProvider`. Many similar services support
overriding the `defaults` object with a new one, but this service only supports changing individual
properties.

Closes #15362

src/ngCookies/cookies.js

@@ -46,6 +46,16 @@ angular.module('ngCookies', ['ng']).
      * Note: By default, the address that appears in your `<base>` tag will be used as the path.
      * This is important so that cookies will be visible for all routes when html5mode is enabled.
      *
+     * @example
+     *
+     * ```js
+     * angular.module('cookiesProviderExample', ['ngCookies'])
+     *   .config(['$cookiesProvider', function($cookiesProvider) {
+     *     // Setting default options
+     *     $cookiesProvider.defaults.domain = 'foo.com';
+     *     $cookiesProvider.defaults.secure = true;
+     *   }]);
+     * ```
      **/
     var defaults = this.defaults = {};