readme: add open with codespaces button (#34)

Author: clstokes

README.md

@@ -2,6 +2,8 @@
 
 [![status: experimental](https://img.shields.io/badge/status-experimental-blue)](https://tailscale.com/kb/1167/release-stages/#experimental)
 
+<a href='https://github.com/codespaces/new?skip_quickstart=true&machine=basicLinux32gb&repo=739163245&ref=main&geo=UsWest&devcontainer_path=.devcontainer%2Fwith-tailscale%2Fdevcontainer.json'><img src='https://github.com/codespaces/badge.svg' alt='Open in GitHub Codespaces with Tailscale' style='max-width: 100%;'></a>
+
 ## Overview
 
 This repository contains Infrastructure as code (IaC) examples for common Tailscale deployments across common infrastructure providers - Amazon Web Services, Azure, and Google Cloud.