usage of pwd

[farbodbj]

The recommended way of running the environment provided in your readme: docker run -it --rm -v $(pwd):/home/xv6/xv6-riscv wtakuo/xv6-env fails in many cases, because the path in which xv6-riscv is located my often include space which when used as $(pwd) causes the whole path to break and create an invalid command. Thus replacing $(pwd) with "$(pwd)" is recommended and will fix the issue. Also to make the script runnable from other directories (when it's in a bash file and is to be launched from elsewhere) I recommend using ${0%/*} instead that will substitute the path where the script is located.