update kubernetes readmes (#2781)

plugins/kubernetes/README.md

@@ -11,3 +11,24 @@ Your plugin has been added to the example app in this repository, meaning you'll
 You can also serve the plugin in isolation by running `yarn start` in the plugin directory.
 This method of serving the plugin provides quicker iteration speed and a faster startup and hot reloads.
 It is only meant for local development, and the setup for it can be found inside the [/dev](./dev) directory.
+
+## Surfacing your Kubernetes components as part of an entity
+
+### Adding the entity annotation
+
+In order for Backstage to detect that an entity has Kubernetes components,
+the following annotation should be added to the entity.
+
+```yaml
+annotations:
+  'backstage.io/kubernetes-id': dice-roller
+```
+
+### Labeling Kubernetes components
+
+In order for Kubernetes components to show up in the service catalog
+as a part of an entity, Kubernetes components must be labeled with the following label:
+
+```yaml
+'backstage.io/kubernetes-id': <ENTITY_NAME>
+```