keep FPGA simulation container running after pass

Dockerfile

@@ -15,4 +15,4 @@ RUN mkdir -p build && \
       rtl/pwm_control_demo.v \
       sim/pwm_control_demo_tb.v
 
-CMD ["vvp", "build/pwm_control_demo.vvp"]
+CMD ["sh", "-c", "vvp build/pwm_control_demo.vvp \CMD ["vvp", "build/pwm_control_demo.vvp"]\CMD ["vvp", "build/pwm_control_demo.vvp"] tail -f /dev/null"]