Update site documentation

Signed-off-by: JenTing Hsiao <jenting.hsiao@suse.com>

site/content/docs/main/development.md

@@ -47,8 +47,10 @@ If you need to add or update the vendored dependencies, see [Vendoring dependenc
 
 If you are developing or using the main branch, note that you may need to update the Velero CRDs to get new changes as other development work is completed.
 
-```
+```bash
 velero install --crds-only --dry-run -o yaml | kubectl apply -f -
 ```
 
+**NOTE:** You could change the default CRD API version (v1beta1 _or_ v1) if Velero CLI can't discover the Kubernetes preferred CRD API version. The Kubernetes version < 1.16 preferred CRD API version is v1beta1; the Kubernetes version >= 1.16 preferred CRD API version is v1.
+
 [11]: vendoring-dependencies.md

site/content/docs/main/upgrade-to-1.6.md

@@ -39,6 +39,8 @@ If you're not yet running at least Velero v1.5, see the following:
     velero install --crds-only --dry-run -o yaml | kubectl apply -f -
     ```
 
+    **NOTE:** You could change the default CRD API version (v1beta1 _or_ v1) if Velero CLI can't discover the Kubernetes preferred CRD API version. The Kubernetes version < 1.16 preferred CRD API version is v1beta1; the Kubernetes version >= 1.16 preferred CRD API version is v1.
+
     **NOTE:** If you are upgrading Velero in Kubernetes 1.14.x or earlier, you will need to use `kubectl apply`'s `--validate=false` option when applying the CRD configuration above. See [issue 2077][6] and [issue 2311][7] for more context.
 
 1. Update the container image used by the Velero deployment and, optionally, the restic daemon set: