Docs feedback: Include reference to Violations-Lib as an alternative to Code Climate

Page: https://docs.gitlab.com/ee/user/project/merge_requests/code_quality.html

What: Suggest that you add a reference to the tool at https://github.com/tomasbjerre/violations-lib as an example of an external custom tool as an alternative to the code climate (seeming) mess.

Why: This tool converts the output of a large number of quality checkers to code climate yaml. It supports Maven, Gradle and command line for build environment.

For anyone migrating from Jenkins (like us) using standard tools (like us), not liking Code Climate at all (like us), then this is perfect. We now have Checkstyle, PMD, SpotBugs, Detekt, etc, etc, all included in the GitLab PR page.