Add build status badge.

README.md

 # Toolbox build
 
+[![pipeline status](https://git.shore.co.il/shore/toolbox-build/badges/master/pipeline.svg)](https://git.shore.co.il/shore/toolbox-build/-/commits/master)
+
 Build [toolbox](https://github.com/containers/toolbox/).
 
 Until there's Debian packaging for it, build it myself.