doc: add example for user-data

doc/reference/autoinstall-reference.rst

@@ -1008,4 +1008,18 @@ user-data
 * **default:** ``{}``
 * **can be interactive:** no
 
-Provide cloud-init user data, which will be merged with the user data the installer produces. If you supply this, you don't need to supply an :ref:`identity section <ai-identity>` (in that case, ensure you can log in to the installed system).
+Provide cloud-init user data, which will be merged with the user data the installer produces. If you supply this, you don't need to supply an :ref:`identity section <ai-identity>` (in that case, ensure you can log in to the installed system). For more details on cloud-init user-data, see :doc:`cloud-init:reference/examples`.
+
+The following user-data is approximately equivalent to what is generated by the example provided in the :ref:`identity section <ai-identity>`:
+
+.. code-block:: yaml
+
+  autoinstall:
+    user-data:
+       users:
+         - name: ubuntu
+           gecos: 'Ubuntu User'
+           passwd: '$6$wdAcoXrU039hKYPd$508Qvbe7ObUnxoj15DRCkzC3qO7edjH0VV7BPNRDYK4QR8ofJaEEF2heacn0QgD.f8pO8SNp83XNdWG6tocBM1'
+           groups: adm, cdrom, dip, lxd, plugdev, sudo
+           shell: /bin/bash
+           lock_passwd: False