Docs Should Live In The Repo

Your documentation should live in the repo with your code. Ideally in docs/. When you write documentation for your service in another system, it quickly becomes disconnected from the repo itself. Any changes made to the code end up being undocumented and the docs that people rely on become outdated. When docs live in the repo, you can view docs that go with that specific version of the code. They are under source control, thus changes can be associated with a specific version of the code. In other words, your docs can be in lock step with your code.