[BUG] make veri_run in the README is missing supporting Makefile and testbenches

Created by: tianrui-wei

Is there an existing CVA6 bug for this?

• I have searched the existing bug issues

Bug Description

The readme.md claims there's a core-only testbench with make veri_run here, but no Makefile or supporting testbench is available. It'd be great if someone could either update the instruction or add the supporting files