Add necessary steps to terraform provider tutorial (hetzneronline#454)

* Add necessary steps

* Adjust line of text

Co-authored-by: Lars Pickelin <[email protected]>

tutorials/howto-hcloud-terraform/01.en.md

@@ -31,11 +31,12 @@ In order to create a Hetzner Cloud API token, please visit Hetzner Cloud Console
 
 ## Step 1 - Basic Usage
 
-First of all, we create a new directory which will contain our Terraform configuration. We will call it `terraform` and create a new file there called `hcloud.tf`. You can name the file as you like.
+First of all, we create a new directory which will contain our Terraform configuration. We will call it `terraform` and create two new files called `hcloud.tf` and `variables.tf`. You can name the files as you like.
 
 ```bash
 mkdir terraform
 touch hcloud.tf
+touch variables.tf
 ```
 
 You can now edit the `hcloud.tf` with a text editor of your choice.
@@ -88,6 +89,37 @@ resource "hcloud_server" "web" {
 
 This short snippet does basically nothing. It just defines a resource from type `hcloud_server` called `web`. But it won't work, because we didn't tell Terraform which server should be created.
 
+You can now edit the `variables.tf` with a text editor of your choice.
+
+We will first copy the following example into the file.
+
+```hcl
+terraform {
+  required_providers {
+    hcloud = {
+      source = "hetznercloud/hcloud"
+    }
+  }
+  required_version = ">= 0.13"
+}
+```
+We will see, what the specific parts mean:
+
+```hcl
+required_providers {
+    hcloud = {
+      source = "hetznercloud/hcloud"
+    }
+}
+```
+Each Terraform module must declare which providers it requires, so that Terraform can install and use them. Provider requirements are declared in a `required_providers` block.
+A provider requirement consists of a local `name` (`hcloud`), a `source` location (`hetznercloud/hcloud`) , and a `version` constraint. In our case, we only add the `source` which forces terraform to use the latest provider version.
+
+```hcl
+  required_version = ">= 0.13"
+```
+The `required_version` setting accepts a version constraint string, which specifies which versions of Terraform can be used with your configuration. in our case, we use v0.13 or higher.
+
 So now you should create a `terraform.tfvars` -file which will contain the following content:
 
 ```text