imapc_sasl_mechanisms: Document supported values

Author: cmouse

data/settings.js

@@ -6583,7 +6583,20 @@ imapc_sasl_mechanisms {
   plain = yes
   login = yes
 }
-\`\`\``
+\`\`\`
+
+Supported mechanisms are:
+
+ * ANONYMOUS
+ * EXTERNAL
+ * LOGIN
+ * OAUTHBEARER
+ * PLAIN
+ * SCRAM-SHA-1
+ * SCRAM-SHA-1-PLUS
+ * SCRAM-SHA-256
+ * SCRAM-SHA-256-PLUS
+ * XOAUTH2`
 	},
 
 	imapc_ssl: {