Add 'how to use the provider' in the README of repo (#341)

* add 'how to use the provider' in the README of repo

* move how to part in Getting started

Author: GokceGK

README.md

@@ -3,9 +3,26 @@
 # Introduction
 
 This project is the official Terraform provider for STACKIT.
-
+        
 # Getting Started
 
+To install STACKIT Terraform Provider, copy and paste this code into your Terraform configuration. Then, run `terraform init`.
+
+```
+terraform {
+  required_providers {
+    stackit = {
+      source = "stackitcloud/stackit"
+      version = "X.X.X"
+    }
+  }
+}
+
+provider "stackit" {
+  # Configuration options
+}
+```
+
 Check one of the examples in the [examples](examples/) folder.
 
 # Authentication