docs(ngAnimateMock): document how to require mocked service in tests

Closes #14668
Closes #14670

Author: Hadrien Tulipe

src/ngMock/angular-mocks.js

@@ -760,6 +760,8 @@ angular.mock.TzDate.prototype = Date.prototype;
  * @description
  * Mock implementation of the {@link ng.$animate `$animate`} service. Exposes two additional methods
  * for testing animations.
+ *
+ * You need to require the `ngAnimateMock` module in your test suite for instance `beforeEach(module('ngAnimateMock'))`
  */
 angular.mock.animate = angular.module('ngAnimateMock', ['ng'])