Clarify examples and read me

quickstart/101-machine-learning/main.tf

@@ -1,6 +1,16 @@
+terraform {
+  required_version = ">=0.15.0"
+
+  required_providers {
+    azurerm = {
+      source  = "hashicorp/azurerm"
+      version = "=2.56.0"
+    }
+  }
+}
+
 provider "azurerm" {
-    version = "~>2.0"
-    features {}
+  features {}
 }
 
 data "azurerm_client_config" "current" {}