Add example for azure function app using key vault reference (#114)

add examples for function app using key vault reference

quickstart/201-function-app-key-vault-ref/variables.tf

@@ -0,0 +1,10 @@
+variable "name_prefix" {
+  type        = string
+  description = "Prefix of the resource name"
+}
+
+variable "location" {
+  type        = string
+  description = "Location to deploy the resource group"
+  default     = "West US 2"
+}