Make it distributable

Hello,

I find this utility very useful nowadays, when people start to host their own 'in house' cloud with NAS, and it's my case. To reduce the power consumption, I found a way to shutdown the NAS at night and needed a way to wake it up without having to touch the power switch in the front end.

This pull request fixes a bug with the -p option and adds :
 - a makefile to build it almost everywhere with make and gcc,
 - a man page to know how to use it on any UNIX system and
 - a README page for Github.

Regards