Discord "logger".

Added a config comment that explains how to use the Slack Logger to hook into Discord.

config/vufind/config.ini

@@ -1192,6 +1192,10 @@ skip_numeric = true
 ;slack = #channel_name:alert,error
 ;slackurl = https://hooks.slack.com/services/your-private-details
 ;slackname = "VuFind Log" ; username messages are posted under
+; You can also use the Slack settings to hook into Discord:
+; - Get your url from Server Settings > Webhooks
+; - Add /slack to the end of your url for Slack-compatible messages
+; https://discordapp.com/developers/docs/resources/webhook#execute-slackcompatible-webhook
 
 ; This section can be used to specify a "parent configuration" from which
 ; the current configuration file will inherit.  You can chain multiple