doc: add badges to README

this is the start of adding badges to show the state and condition of the repo.

https://www.freecodecamp.org/news/how-to-use-badges-to-stop-feeling-like-a-noob-d4e6600d37d2/

README.md

@@ -1,3 +1,5 @@
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+
 ![piku logo](./img/logo.png)
 
 The tiniest Heroku/CloudFoundry-like PaaS you've ever seen.