Try using google to search the site. This has been discussed a number of times.
A few people go to the trouble of putting slip rings into the design. But most just let the wire hang down the tower with a bit of slack and include a weatherproof plug-outlet combo near the base.
Unless you have a turbulent site (or a dust devil sits on the mill for a while) the mill will mostly turn back-and-forth as the wind shifts but not spin around and wind up the cord. Every few months (on a calm day so it won't run away while you're futzing with it) you unplug the mill, plug in a shorting plug to keep it from taking off, unwind any accumulated full-turns, and plug it back in.
You probably don't want to depend on this method if the mill is unattended for months at a time, like at a vacation home. But if it's where you live you should be fine. Check it every few days, then every few weeks and after any big storms, to see how it behaves. Eventually you'll have a good idea of how often your particular site and mill needs unwinding (like maybe three or four times a year or less if your site is typical).
