README.md: Add GitHub star history chart

... from https://star-history.com/.

#1511

Author: debarshiray

README.md

@@ -46,6 +46,11 @@ See our guides on
 Toolbx and [Linux distro support](https://containertoolbx.org/distros/).
 
 
+##
+
+[![Star History Chart](https://api.star-history.com/svg?repos=containers/toolbox&type=Date)](https://star-history.com/#containers/toolbox&Date)
+
+
 ##
 
 [![Zuul](https://zuul-ci.org/gated.svg)](https://softwarefactory-project.io/zuul/t/local/builds?project=containers/toolbox)