docs(guide/e2e-testing): callout ngmodel vs attr
docs(guide/e2e-testing): callout ngmodel vs attr

Add note that `input()` fn matches ng-model instead of HTML name attribute.
About five users on forums were snagged by this assumption:
http://docs.angularjs.org/guide/dev_guide.e2e-testing#comment-898079915

Closes #4655

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js