Update documentation on service annotations

docs/reference.md

@@ -2233,6 +2233,37 @@ The LVs are created in the volume specified by the `volumes_vg` global
 configuration variable, which by default is *vg0*. The VG must already
 exist, float will not attempt to create it.
 
+### Annotations
+
+`annotations`: Dictionary with service-specific annotations
+
+Annotations are manually curated metadata associated with the service,
+intended for debugging purposes. This is data meant for humans to
+consume, with the idea of helping the operators understand and debug
+your services and their interconnections.
+
+Annotations are for now only displayed on the float admin dashboard.
+
+`summary`: A short summary (description) of the service.
+
+#### Dependency graphs
+
+`dependencies`: A list of additional service dependencies.
+
+Float can automatically compute part of the dependency graph between
+your services, at least insofar as the structure of *public_endpoints*
+is concerned. Since this data can be quite useful in understanding the
+structure of a service, it is possible to extend the dependency graph
+manually by specifying additional edges (representing the dependencies
+between services).
+
+Edges of the dependency graphs are specified as objects with `client`
+and `server` attributes, identifying a specific container or systemd
+unit in either the current service or a different one. If you're
+referring to an entity within the same service, you can just use its
+name, while for external services the syntax is
+*service-name*/*entity-name* (e.g. "log-collector/elasticsearch").
+
 ### Examples
 
 Let's look at some example *services.yml* files: