Fix the dpp_configurator_sign example command

The mandatory ssid parameter was forgotten from this command when it was
added to the dpp_auth_init examples.

Signed-off-by: Jouni Malinen <j@w1.fi>

wpa_supplicant/README-DPP

@@ -156,7 +156,7 @@ command to get DPP credentials.
 
 > dpp_configurator_add
 (returns configurator id)
-> dpp_configurator_sign conf=<ap-dpp|sta-dpp> configurator=<configurator-id>
+> dpp_configurator_sign conf=<ap-dpp|sta-dpp> configurator=<configurator-id> ssid=<SSID hexdump>
 
 
 Sample AP configuration files after provisioning