Readme update.
Readme update.

- Typos.
- Tutorial online link.

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