Example output lacks mandatory member @timestamp.  Provide it.

Event's documentation is not properly formatted. Fix it by:
- Adding @ to "device-id"
- Adding extra line for "Since" section

Signed-off-by: Victor Toso <victortoso@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-Id: <20220328140604.41484-9-victortoso@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>