docs(input[checkbox]): mention ngChecked

Closes angular#14465
Closes angular#15277

Author: vgvenkat

src/ng/directive/input.js

@@ -1112,6 +1112,9 @@ var inputType = {
    *                  Can be interpolated.
    * @param {string=} ngChange Angular expression to be executed when the ngModel value changes due
    *                  to user interaction with the input element.
+   * @param {expression=} ngChecked If the expression is truthy, then the `checked` attribute will be set on the
+   *                      element. **Note** : `ngChecked` should not be used alongside `ngModel`.
+   *                      Checkout {@link ng.directive:ngChecked ngChecked} for usage.
    *
    * @example
       <example name="range-input-directive" module="rangeExample">