README: Add CII Best Practices badge

Author: daurnimator

README.md

@@ -19,6 +19,7 @@ Can be found at [https://daurnimator.github.io/lua-http/](https://daurnimator.gi
 
 [![Build Status](https://travis-ci.org/daurnimator/lua-http.svg)](https://travis-ci.org/daurnimator/lua-http)
 [![Coverage Status](https://coveralls.io/repos/daurnimator/lua-http/badge.svg?branch=master&service=github)](https://coveralls.io/github/daurnimator/lua-http?branch=master)
+[![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/108/badge)](https://bestpractices.coreinfrastructure.org/projects/108)
 
 
 # Installation