add pod generation to docs

Author: natasha41575

Diff for: content/en/docs/concepts/workloads/pods/_index.md

@@ -226,9 +226,13 @@ like
 have some limitations:
 
 - Most of the metadata about a Pod is immutable. For example, you cannot
-  change the `namespace`, `name`, `uid`, or `creationTimestamp` fields;
-  the `generation` field is unique. It only accepts updates that increment the
-  field's current value.
+  change the `namespace`, `name`, `uid`, or `creationTimestamp` fields.
+    - The `generation` field is unique. It will be automatically set by the
+      system such that new pods have a `generation` of 1, and every update to
+      mutable fields in the pod's spec will increment the `generation` by 1. If the
+      alpha feature gate PodObservedGenerationTracking is set, the
+      pod's `status.observedGeneration` will reflect the `metadata.generation` of
+      the pod at the point that the pod status is being reported.
 - If the `metadata.deletionTimestamp` is set, no new entry can be added to the
   `metadata.finalizers` list.
 - Pod updates may not change fields other than `spec.containers[*].image`,