docs(kubectl-trace): screenshot showing the program

Signed-off-by: Lorenzo Fontana <[email protected]>

Author: fntlnz

README.md

@@ -3,6 +3,7 @@
 `kubectl trace` is a kubectl plugin that allows you to schedule the execution
 of [bpftrace](https://github.com/iovisor/bpftrace) programs in your Kubernetes cluster.
 
+![Screenshot showing the read.bt program for kubectl-trace](docs/img/intro.png)
 
 ## Installation