docs(identity): add example

Closes #14528

Author: dotku

src/Angular.js

@@ -445,12 +445,22 @@ noop.$inject = [];
  * functional style.
  *
    ```js
-     function transformer(transformationFn, value) {
-       return (transformationFn || angular.identity)(value);
-     };
+   function transformer(transformationFn, value) {
+     return (transformationFn || angular.identity)(value);
+   };
+
+   // E.g.
+   function getResult(fn, input) {
+     return (fn || angular.identity)(input);
+   };
+
+   getResult(function(n) { return n * 2; }, 21);   // returns 42
+   getResult(null, 21);                            // returns 21
+   getResult(undefined, 21);                       // returns 21
    ```
-  * @param {*} value to be returned.
-  * @returns {*} the value passed in.
+ *
+ * @param {*} value to be returned.
+ * @returns {*} the value passed in.
  */
 function identity($) {return $;}
 identity.$inject = [];