message: Point to ADR instead of issue for catalog kinds
diff: @@ -79,11 +79,14 @@ The root envelope object has the following structure.
  ### `apiVersion` and `kind` [required]
  -The `kind` is the high level entity type being described. The
  -[Backstage system model](https://github.com/spotify/backstage/issues/390) describes
  +The `kind` is the high level entity type being described.
  +[ADR005](/docs/architecture-decisions/adr005-catalog-core-entities.md) describes
  a number of core kinds that plugins can know of and understand, but an organization
  using Backstage is free to also add entities of other kinds to the catalog.
  +The perhaps most central kind of entity, that the catalog focuses on in the initial
  +phase, is `Component` ([see below](#kind-component)).
  +
  The `apiVersion` is the version of specification format for that particular
  entity that the specification is made against. The version is used for being able to
  evolve the format, and the tuple of `apiVersion` and `kind` should be enough
  