Add CII Best Practices badge

A reminder to focus on project quality.

README.md

@@ -6,6 +6,8 @@ OliveTin gives **safe** and **simple** access to predefined shell commands from
 
 [![Discord](https://img.shields.io/discord/846737624960860180?label=Discord%20Server)](https://discord.gg/jhYWWpNJ3v)
 [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38d29fed78fa85652e3a63e154dd8e8829/media/badge.svg)](https://github.com/awesome-selfhosted/awesome-selfhosted#automation)
+[![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/5050/badge)](https://bestpractices.coreinfrastructure.org/projects/5050)
+
 [![Go Report Card](https://goreportcard.com/badge/github.com/Olivetin/OliveTin)](https://goreportcard.com/report/github.com/OliveTin/OliveTin)
 [![Build Snapshot](https://github.com/OliveTin/OliveTin/actions/workflows/build-snapshot.yml/badge.svg)](https://github.com/OliveTin/OliveTin/actions/workflows/build-snapshot.yml)