installing nodejs module doesnt give me the command

I am trying to run pixel-ping and running into trouble. I followed these instructions:

http://documentcloud.github.io/pixel-ping/ and it mentions that Installing Pixel Ping gives you the pixel-ping command. but when I type pixel-ping path/to/config.json it returns -bash: pixel-ping: command not found I am not sure why it would say that any ideas would be greatly appreciated. I have both nodejs and npm installed I have other modules working perfectly. Am I doing something wrong ?