You may have wiki style documentation in your GitLab project. It all depends on exactly what your goals are. Often, the most common thing we hear from other Shared Tools customers is that neither of these features beats the simplicity of putting Markdown files in the repository itself and using those files as your documentation.

• Gitlab has a Wiki feature: https://docs.gitlab.com/ee/user/project/wiki/
• Gitlab also has a feature called Snippets: https://docs.gitlab.com/ee/user/snippets.html.