Add docs for the tracing mvc

doc/user/project/operations/tracing.md

+# Tracing **[ULTIMATE]**
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7903) in GitLab Ultimate 11.5.
+
+Tracing provides insight into the performance and health of a deployed application,
+tracking each function or microservice which handles a given request.
+
+This makes it easy to
+understand the end-to-end flow of a request, regardless of whether you are using a monolithic or distributed system.
+
+## Jaeger tracing
+
+[Jaeger](https://www.jaegertracing.io/) is an open source, end-to-end distributed
+tracing system used for monitoring and troubleshooting microservices-based distributed
+systems.
+
+### Deploying Jaeger
+
+To learn more about deploying Jaeger, read the official
+[Getting Started documentation](https://www.jaegertracing.io/docs/latest/getting-started/).
+There is an easy to use [all-in-one Docker image](https://www.jaegertracing.io/docs/latest/getting-started/#AllinoneDockerimage),
+as well as deployment options for [Kubernetes](https://github.com/jaegertracing/jaeger-kubernetes)
+and [OpenShift](https://github.com/jaegertracing/jaeger-openshift).
+
+### Enabling Jaeger
+
+GitLab provides an easy way to open the Jaeger UI from within your project:
+
+1. [Set up Jaeger](#deploying-jaeger) and configure your application using one of the
+   [client libraries](https://www.jaegertracing.io/docs/latest/client-libraries/).
+1. Navigate to your project's **Settings > Operations** and provide the Jaeger URL.
+1. Click **Save changes** for the changes to take effect.
+1. You can now visit **Operations > Tracing** in your project's sidebar and
+   GitLab will redirect you to the configured Jaeger URL.
\ No newline at end of file

doc/user/project/settings/index.md

@@ -120,3 +120,9 @@ GitLab administrators can use the admin interface to move any project to any
 namespace if needed.
 
 [permissions]: ../../permissions.md##project-members-permissions
+
+## Operations settings
+
+### Jaeger tracing
+
+Add the URL of a Jaeger server to allow your users to [easily access the Jaeger UI from within GitLab](../operations/tracing.md).