bootstrap: Add additional context of bootstrap pod manifest in comments

The installer renders the CVO bootstrap manifests into its
bootstrap-manifests directory [1], where bootstrap manifests of other
related componenets are rendered as well by their respective bootstrap
commands.

The directory is then consumed by the cluster-bootstrap component [2].
The cluster-bootstrap component copies these manifests to the static
Pod path of the node's kubelet [3].

As such, static Pods have some notable details, such as:

> The spec of a static Pod cannot refer to other API objects
> (e.g., ServiceAccount, ConfigMap, Secret, etc). [4]

Mention this in the manifest to save some time for future developers.

[1]: https://github.com/openshift/installer/blob/c93ae9fc74d7fa0f478fa250de2ba702f84a0a21/data/data/bootstrap/files/usr/local/bin/bootkube.sh.template#L192
[2]: https://github.com/openshift/installer/blob/c93ae9fc74d7fa0f478fa250de2ba702f84a0a21/data/data/bootstrap/files/usr/local/bin/bootkube.sh.template#L576
[3]: https://github.com/openshift/cluster-bootstrap/blob/dc0d4a5cdaf8a7477cab584208dc99352f46efe2/pkg/start/bootstrap.go#L52-L60
[4]: https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/

Author: DavidHurta

bootstrap/bootstrap-pod.yaml

@@ -1,3 +1,6 @@
+# This Pod manifest is deployed as a static Pod via kubelet during cluster bootstrapping.
+# Static Pods are managed directly by kubelet and cannot reference API objects like
+# ServiceAccount, ConfigMap, or Secret in their spec.
 apiVersion: v1
 kind: Pod
 metadata: