docs($templateRequest): update the description with caching changes

The previous changes to $templateRequest were not documented, they now are.

Author: rjamet

src/ng/templateRequest.js

@@ -7,10 +7,12 @@ var $compileMinErr = minErr('$compile');
  * @name $templateRequest
  *
  * @description
- * The `$templateRequest` service downloads the provided template using `$http` and, upon success,
- * stores the contents inside of `$templateCache`. If the HTTP request fails or the response data
- * of the HTTP request is empty, a `$compile` error will be thrown (the exception can be thwarted
- * by setting the 2nd parameter of the function to true).
+ * The `$templateRequest` service runs security checks then downloads the provided template using
+ * `$http` and, upon success, stores the contents inside of `$templateCache`. If the HTTP request
+ * fails or the response data of the HTTP request is empty, a `$compile` error will be thrown (the
+ * exception can be thwarted by setting the 2nd parameter of the function to true). Note that the
+ * contents of `$templateCache` are trusted, so the call to `$sce.getTrustedUrl(tpl)` is omitted
+ * when `tpl` is of type string and `$templateCache` has the matching entry.
  *
  * @param {string|TrustedResourceUrl} tpl The HTTP request template URL
  * @param {boolean=} ignoreRequestError Whether or not to ignore the exception when the request fails or the template is empty