docs: added description and usage

Author: robinlieb

README.md

@@ -1 +1,15 @@
-# terraform-kubeadm-token
+# Terraform token for kubeadm
+
+Terraform module designed to generate a token for kubeadm. The generated token will be in the format <token_id>.<token_secret> and maches the regular expression "[a-z0-9]{6}.[a-z0-9]{16}".
+
+## Usage
+
+```hcl
+module "kubeadm_token" {
+  source  = "robinlieb/terraform-kubeadm-token"
+}
+
+output "token" {
+  value = module.kubeadm_token.token
+}
+```