Remove duplicated link

doc/README.md

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 - [Project Services](project_services/project_services.md) Integrate a project with external services, such as CI and chat.
 - [Public access](public_access/public_access.md) Learn how you can allow public and internal access to projects.
 - [Analytics](analytics/README.md)
-- [Container Registry](container_registry/README.md) Learn how to use GitLab Container Registry.
 - [SSH](ssh/README.md) Setup your ssh keys and deploy keys for secure access to your projects.
 - [Webhooks](web_hooks/web_hooks.md) Let GitLab notify you when new code has been pushed to your project.
 - [Workflow](workflow/README.md) Using GitLab functionality and importing projects from GitHub and SVN.