Add information for easily running commands

[jackadanos]

Hello,

Thank you for developing this program! I just used it to connect to my RT-21 Az/El controller. One suggestions I have is to add instructions for an easy way to connect to the greenctld port and manually run commands. I used the following command:
nc localhost 4533
And then you can enter in your commands such as "p", "P 150 20", or "S".

This is something that experienced users probably don't need help with, but for novices like me it was a bit unclear how to actually get the rotator to move via manual commands after running the greenctld program!