storage: Show how to create admin password secret

storage/README.md

@@ -23,6 +23,15 @@ kubectl apply -f longhorn.yaml
 Expose the Longhorn UI outside the cluster:
 
 ```sh
+printf 'Longhorn username: '
+read longhorn_username
+printf 'Longhorn password: '
+read -s longhorn_password
+printf '%s:%s\n' \
+    "${longhorn_username}" \
+    "$(openssl passwd -stdin -apr1 <<< "${longhorn_password}")" \
+    > auth
+kubectl create secret generic -n longhorn-system basic-auth --from-file auth
 kubectl apply -f longhorn-ingress.yaml
 ```