chore: Add badge for latest version number (#384)

Author: christoph-buente

README.md

@@ -1,6 +1,8 @@
 # AWS VPC Terraform module
 
 [![Help Contribute to Open Source](https://www.codetriage.com/terraform-aws-modules/terraform-aws-vpc/badges/users.svg)](https://www.codetriage.com/terraform-aws-modules/terraform-aws-vpc)
+![GitHub tag (latest by date)](https://img.shields.io/github/v/tag/terraform-aws-modules/terraform-aws-vpc)
+
 
 Terraform module which creates VPC resources on AWS.