content: Fix VM start command

Previous command used to start VM is missing image as its parameter, add
default image name as its parameter.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

Author: RuoqingHe

src/virtualization/cloud-hypervisor/heterogeneous-runner.md

@@ -124,7 +124,7 @@ to be the development environment because its kernel version does not support
 AIA. With this script in place, you can start VM with command:
 
 ```sh
-bash start-riscv64.sh
+bash start-riscv64.sh ubuntu-24.04.1-preinstalled-server-riscv64.img
 ```
 
 ### Guest