Document behavior on internal networks - empty lookup results

I might be an isolated idiot case, but I just ran across this interesting bit of behavior... GeoIP API (and really any GeoIP-type library) returns a NULL/empty result set on internal networks that are running in private address ranges, defined here:

http://en.wikipedia.org/wiki/Private_network

By definition, these ranges are not registered to any ISP, and therefore have no location data - and can be located anywhere.

This might be a good thing to document in INSTALL.txt so someone developing on an internal server doesn't beat their head against the nearest hard surface, repeatedly, for a few minutes. Oh, and along the same lines letting users know that is where the geoip_debug comes into play (as well as for testing remote locations).

Thanks!