Document to to specify libraries by hand.
Document to to specify libraries by hand.

Pull request #29 introduced an way for the application specify the
location of the underline backend library.

This is useful when PyUSB cannot find the library automatically.

karlp/pyusb,makerbot/pyusb,kopchik/pyusb,kopchik/pyusb,h3nj3/pyusb,swinman/pyusb,karlp/pyusb,swinman/pyusb,rabryan/pyusb,AlanJAS/pyusb,h3nj3/pyusb,rabryan/pyusb,makerbot/pyusb,AlanJAS/pyusb