message: docs(plugins/pagerduty): update README for new annotation support
diff: - The Backstage PagerDuty plugin allows PagerDuty information about a Backstage entity to be displayed within Backstage. This includes active incidents, recent change events, as well as the current on-call responders' names, email addresses, and links to their profiles in PagerDuty.
  - Incidents can be manually triggered via the plugin with a user-provided description, which will in turn notify the current on-call responders.
  + - _Note: This feature is only available when providing the `pagerduty.com/integration-key` annotation_
  - Change events will be displayed in a separate tab. If the change event payload has additional links the first link only will be rendered.
  # Requirements
  @@ -117,6 +118,26 @@ This will proxy the request by adding an `Authorization` header with the provide
  ### Optional configuration
  +#### Annotating with Service ID
  +
  +If you want to integrate a PagerDuty service with Backstage but don't want to use an integration key, you can also [annotate](https://backstage.io/docs/features/software-catalog/descriptor-format#annotations-optional) the appropriate entity with a PagerDuty Service ID instead
  +
  +```yaml
  +annotations:
  + pagerduty.com/service-id: [SERVICE_ID]
  +```
  +
  +This service ID can be found by navigating to a Service within PagerDuty and pulling the ID value out of the URL.
  +
  +1. From the **Configuration** menu within PagerDuty, select **Services**.
  +2. Click the **name** of the service you want to represent for your Entity.
  +
  +Your browser URL should now be located at `https://pagerduty.com/service-directory/[SERVICE_ID]`.
  +
  +_Note: When annotating with `pagerduty.com/service-id`, the feature to Create Incidents is not currently supported_
  +
  +#### Custom Events URL
  +
  If you want to override the default URL used for events, you can add it to `app-config.yaml`:
  ```yaml
  