[processor/k8sattributes] Update README.md (#34950)

**Documentation:**

Update README for Kubernetes Attributes Processor to indicate
`container.id` attribute is available if `k8s.container.name` is
provided.
I followed
https://docs.appdynamics.com/observability/cisco-cloud-observability/en/application-performance-monitoring/monitor-applications-in-kubernetes/infrastructure-correlation#InfrastructureCorrelation-KubernetesPodContainerID
and it's working.

cc @iskiselev

---------

Co-authored-by: Alex Boten <223565+codeboten@users.noreply.github.com>

processor/k8sattributesprocessor/README.md

@@ -102,6 +102,7 @@ Additional container level attributes can be extracted provided that certain res
    - container.image.tag
    - container.image.repo_digests (if k8s CRI populates [repository digest field](https://github.com/open-telemetry/semantic-conventions/blob/v1.26.0/model/registry/container.yaml#L60-L71))
 2. If the `k8s.container.name` resource attribute is provided, the following additional attributes will be available:
+   - container.id (if the `k8s.container.restart_count` resource attribute is not provided, it's not guaranteed to get the right container ID.)
    - container.image.name
    - container.image.tag
    - container.image.repo_digests (if k8s CRI populates [repository digest field](https://github.com/open-telemetry/semantic-conventions/blob/v1.26.0/model/registry/container.yaml#L60-L71))