Link features to new docs/pages
Update https://about.gitlab.com/features/:
- Service Desk - link to https://about.gitlab.com/features/service-desk/
- Powerful Issue Tracker - link to https://docs.gitlab.com/ee/user/project/issues/
- Work-in-Progress Protection - link to https://docs.gitlab.com/ee/user/project/merge_requests/work_in_progress_merge_requests.html
- Group levels milestones - link to https://docs.gitlab.com/ee/user/project/milestones/index.html#creating-a-group-milestone
- Burndown charts - link to https://docs.gitlab.com/ee/user/project/milestones/burndown_charts.html
- Multiple Assignees - link to https://docs.gitlab.com/ee/user/project/issues/multiple_assignees_for_issues.html
- Multi-Project Pipeline Graphs - link to https://docs.gitlab.com/ee/ci/multi_project_pipeline_graphs.html
Edited by Achilleas Pipinellis