fix: add placeholder for add users

i18n/en_US.yaml

@@ -1430,6 +1430,7 @@ ui:
         fields:
           users:
             label: Bulk add user
+            placeholder: "John Smith, john@example.com, BUSYopr2 \n Alice, alice@example.com, fpDntV8q"
             text: Separate “name, email, password” with commas. One user per line.
             msg: "Please enter the user's email, one per line."
           display_name:

ui/src/hooks/useUserModal/index.tsx

@@ -38,6 +38,7 @@ const useAddUserModal = (props: IProps = {}) => {
       'ui:widget': 'textarea',
       'ui:options': {
         rows: 6,
+        placeholder: t('form.fields.users.placeholder'),
       },
     },
   };