Merge branch 'update-def-of-done-with-qa-tests-requirement' into 'master'

docs - Update definition of done with e2e tests requirement

Closes gitlab-org/quality/team-tasks#67

See merge request gitlab-org/gitlab-ce!22655

doc/development/contributing/merge_request_workflow.md

@@ -171,6 +171,7 @@ the feature you contribute through all of these steps.
 1. Added to [the website](https://gitlab.com/gitlab-com/www-gitlab-com/), if relevant
 1. Community questions answered
 1. Answers to questions radiated (in docs/wiki/support etc.)
+1. [Black-box tests/end-to-end tests](../testing_guide/testing_levels.md#black-box-tests-or-end-to-end-tests) added if required. Please contact [the quality team](https://about.gitlab.com/handbook/engineering/quality/#teams) with any questions  
 
 If you add a dependency in GitLab (such as an operating system package) please
 consider updating the following and note the applicability of each in your