Add wiki link for pfsense_default_gateway

Author: opoplawski

README.md

@@ -65,6 +65,7 @@ The following modules are currently available:
 * [pfsense_authserver_radius](https://github.com/pfsensible/core/wiki/pfsense_authserver_radius) for RADIUS authentication servers
 * [pfsense_ca](https://github.com/pfsensible/core/wiki/pfsense_ca) for Certificate Authorities
 * [pfsense_cert](https://github.com/pfsensible/core/wiki/pfsense_cert) for Certificates
+* [pfsense_default_gateway](https://github.com/pfsensible/core/wiki/pfsense_default_gateway) for setting the default gateways
 * [pfsense_dhcp_static](https://github.com/pfsensible/core/wiki/pfsense_dhcp_static) for static DHCP entries
 * [pfsense_gateway](https://github.com/pfsensible/core/wiki/pfsense_gateway) for routing gateways
 * [pfsense_group](https://github.com/pfsensible/core/wiki/pfsense_group) for user groups