trivial: Add CI status badge to README

Author: ximion

README.md

@@ -1,6 +1,8 @@
 # PackageKit-Qt
 Qt bindings for PackageKit
 
+[![Build Test](https://github.com/PackageKit/PackageKit-Qt/actions/workflows/build-test.yml/badge.svg)](https://github.com/PackageKit/PackageKit-Qt/actions/workflows/build-test.yml)
+
 ## PackageKit
 PackageKit is a DBUS abstraction layer that allows the session user to manage
 packages in a secure way using a cross-distro, cross-architecture API.