reordered variables to make more readable and added documentation

nodes/main.tf

+# is created in internal-network module and called in root module
+variable "internal_subnet_id" {type = string}
+
 variable "image_compute" {}
 variable "flavor" {}
+
+# is created in key-pair module and called in root module
+variable "key_pair" {type = "string"}
+
 variable "compute_node_count" { }
 variable "internal_net" {}
-variable "key_pair" {type = "string"}
-variable "internal_subnet_id" {type = string}
+
+
 
 # creates compute node
 resource "openstack_compute_instance_v2" "c0" {