docs: Update example w/ multi VPC association for r/aws_route53_zone

Author: acwwat

website/docs/r/route53_zone.html.markdown

@@ -55,11 +55,28 @@ resource "aws_route53_record" "dev-ns" {
 ~> **NOTE:** Private zones require at least one VPC association at all times.
 
 ```terraform
+resource "aws_vpc" "primary" {
+  cidr_block           = "10.6.0.0/16"
+  enable_dns_hostnames = true
+  enable_dns_support   = true
+}
+
+resource "aws_vpc" "secondary" {
+  cidr_block           = "10.7.0.0/16"
+  enable_dns_hostnames = true
+  enable_dns_support   = true
+}
+
 resource "aws_route53_zone" "private" {
   name = "example.com"
 
   vpc {
-    vpc_id = aws_vpc.example.id
+    vpc_id = aws_vpc.primary.id
+  }
+
+  # Add multiple `vpc` blocks to associate additional VPCs
+  vpc {
+    vpc_id = aws_vpc.secondary.id
   }
 }
 ```