doc: use scaleway_lb_ip for ip_ids of a scaleway_lb

Author: ahamez

docs/resources/lb.md

@@ -161,6 +161,8 @@ The following arguments are supported:
 
 - `ip_ids` - (Optional) The List of IP IDs to attach to the Load Balancer.
 
+~> **Important:** Make sure to use a [`scaleway_lb_ip`](../lb_ip.md) resource to create the IPs.
+
 - `ip_id` - (Deprecated) The ID of the associated Load Balancer IP. See below.
 
 ~> **Important:** Updates to `ip_id` will recreate the Load Balancer.