docs(filter/uppercase): add an example

I saw that the uppercase filter had no example so I decided to add a minimal example to explain how the uppercase filter works.

Thank you very much to @narretz for helping me through this process.

Closes #15885

src/ng/filter/filters.js

@@ -698,6 +698,9 @@ function jsonFilter() {
  * @kind function
  * @description
  * Converts string to lowercase.
+ *
+ * See the {@link ng.uppercase uppercase filter documentation} for a functionally identical example.
+ *
  * @see angular.lowercase
  */
 var lowercaseFilter = valueFn(lowercase);
@@ -709,6 +712,22 @@ var lowercaseFilter = valueFn(lowercase);
  * @kind function
  * @description
  * Converts string to uppercase.
- * @see angular.uppercase
+ * @example
+   <example module="uppercaseFilterExample" name="filter-uppercase">
+     <file name="index.html">
+       <script>
+         angular.module('uppercaseFilterExample', [])
+           .controller('ExampleController', ['$scope', function($scope) {
+             $scope.title = 'This is a title';
+           }]);
+       </script>
+       <div ng-controller="ExampleController">
+         <!-- This title should be formatted normally -->
+         <h1>{{title}}</h1>
+         <!-- This title should be capitalized -->
+         <h1>{{title | uppercase}}</h1>
+       </div>
+     </file>
+   </example>
  */
 var uppercaseFilter = valueFn(uppercase);