fix username param description

Author: LogExE

net/ddns-scripts/Makefile

@@ -280,7 +280,7 @@ endef
 define Package/ddns-scripts-beget/description
   Dynamic DNS Client scripts extension for 'beget.com'.
   It requires:
-  'option username' to be a valid subdomain for beget.com
+  'option username' to be a valid username for beget.com
   'option password' to be a valid API key for beget.com
 endef