docs(NgModelController): clarify documentation of $setViewValue

$setViewValue does not really "Read a value from view".
It should be called to trigger the ngModel to be updated when the value in the view changes.

Closes #4907

Author: hupf

src/ng/directive/input.js

@@ -1103,14 +1103,19 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
    * @methodOf ng.directive:ngModel.NgModelController
    *
    * @description
-   * Read a value from view.
+   * Update the view value.
    *
-   * This method should be called from within a DOM event handler.
-   * For example {@link ng.directive:input input} or
+   * This method should be called when the view value changes, typically from within a DOM event handler.
+   * For example {@link ng.directive:input input} and
    * {@link ng.directive:select select} directives call it.
    *
-   * It internally calls all `$parsers` (including validators) and updates the `$modelValue` and the actual model path.
-   * Lastly it calls all registered change listeners.
+   * It will update the $viewValue, then pass this value through each of the functions in `$parsers`,
+   * which includes any validators. The value that comes out of this `$parsers` pipeline, be applied to
+   * `$modelValue` and the **expression** specified in the `ng-model` attribute.
+   * 
+   * Lastly, all the registered change listeners, in the `$viewChangeListeners` list, are called.
+   *
+   * Note that calling this function does not trigger a `$digest`.
    *
    * @param {string} value Value from the view.
    */