generic ephemeral volumes: beta

The feature is scheduled for becoming beta in 1.21.

content/en/docs/concepts/storage/ephemeral-volumes.md

@@ -131,9 +131,10 @@ As a cluster administrator, you can use a [PodSecurityPolicy](/docs/concepts/pol
 ### Generic ephemeral volumes
 
 {{< feature-state for_k8s_version="v1.19" state="alpha" >}}
+{{< feature-state for_k8s_version="v1.21" state="beta" >}}
 
 This feature requires the `GenericEphemeralVolume` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) to be
-enabled. Because this is an alpha feature, it is disabled by default.
+enabled. Because this is a beta feature, it is enabled by default.
 
 Generic ephemeral volumes are similar to `emptyDir` volumes, just more
 flexible:
@@ -242,9 +243,7 @@ PVCs indirectly if they can create Pods, even if they do not have
 permission to create PVCs directly. Cluster administrators must be
 aware of this. If this does not fit their security model, they have
 two choices:
-- Explicitly disable the feature through the feature gate, to avoid
-  being surprised when some future Kubernetes version enables it
-  by default.
+- Explicitly disable the feature through the feature gate.
 - Use a [Pod Security
   Policy](/docs/concepts/policy/pod-security-policy/) where the
   `volumes` list does not contain the `ephemeral` volume type.