Update README.md

In the docs it mentions to use killall launchd_sim, but this only works if you closed the application prior to running the command and ocassionally i've seen the services not exit in certain conditions.

Suggest to replace it with

sudo ps -A | grep -e "launchd_sim" -e "simulator" -i | grep -v grep | awk '{print $1}' | xargs kill -9