Add comments explaining where the cidr blocks are coming from

Prior to this commit we had a list of cidr blocks that are used
for ingress to redpanda, but there was no explanation about where
these 'magic' blocks were coming from or what they represent.

Added some comments and included a link to the documentation.

Author: frenchfrywpepper

customer-managed/aws/terraform/security_groups.tf

@@ -64,12 +64,22 @@ resource "aws_security_group" "redpanda_node_group" {
 
 locals {
   rp_node_group_cidr_blocks = var.public_cluster ? [
+
+    // only used in the event that you want a public cluster, when the variable public_cluster is true
     "0.0.0.0/0"
+
     ] : [
+
+    // RFC 6598 reserved prefix for shared address space
+    // https://datatracker.ietf.org/doc/html/rfc6598
     "100.64.0.0/10",
+
+    // RFC 1918 reserved IP address space for private internets
+    // https://datatracker.ietf.org/doc/html/rfc1918
     "172.16.0.0/12",
     "192.168.0.0/16",
     "10.0.0.0/8",
+
   ]
 }
 resource "aws_security_group_rule" "redpanda_node_group" {