say-hello1 v1.0.0

1. we are telling *nix systems that the interpreter of our JavaScript file should be /usr/bin/env node which looks up for the locally-installed node executable.
2. chmod +x cli.
3. try to run ./cli.js haha lala gaga for an example
4. run npm link to make our say-hello1 command executable anywhere
5. try say-hello1 haha lala gaga
6. run npm unlink to disable it from executable, run say-hello1 again will generate error.

Notes: On install, npm will symlink … files into prefix/bin for global installs, or ./node_modules/.bin/ for local installs.