aws/docs: Add example of aws_alb_target_group (#8311)

website/source/docs/providers/aws/r/alb_target_group.html.markdown

@@ -15,6 +15,16 @@ resources.
 ## Example Usage
 
 ```
+resource "aws_alb_target_group" "test" {
+  name     = "tf-example-alb-tg"
+  port     = 80
+  protocol = "HTTP"
+  vpc_id   = "${aws_vpc.main.id}"
+}
+
+resource "aws_vpc" "main" {
+    cidr_block = "10.0.0.0/16"
+}
 ```
 
 ## Argument Reference