added enable-dhcp vars to have a default of true

vars.tf

@@ -15,4 +15,10 @@ variable "keypair-name" {
 }
 
 variable "public-key" {
-  default = "${file("~/.ssh/id_rsa.pub")}"
\ No newline at end of file
+  default = "${file("~/.ssh/id_rsa.pub")}"
+  }
+  
+variable "enable-dhcp" {
+  description = "whether dhcp in enabled. defualt is true"
+  default = true
+  }
\ No newline at end of file