Handle Atheme NickServ IDENTIFY NOTICE

Update list of nickserv identify patterns to support Atheme (
https://github.com/atheme/atheme/blob/master/modules/nickserv/main.c#L80
), used by libera.chat .

Signed-off-by: Luca Bigliardi <shammash@google.com>

config.go

@@ -69,6 +69,7 @@ func LoadConfig(configFile string) (*Config, error) {
 		UsePrivmsg:      false,
 		AlertBufferSize: 2048,
 		NickservIdentifyPatterns: []string{
+			"Please choose a different nickname, or identify via",
 			"identify via /msg NickServ identify <password>",
 			"type /msg NickServ IDENTIFY password",
 			"authenticate yourself to services with the IDENTIFY command",