Place the SR74HC595 library folder into your \Documents\Arduino\libraries folder. You may need to create the libraries subfolder if its your first library. Restart the IDE.

It is possible that I can use the USARTs on the Teensy 3/3.1 and Arduino Due for SPI as well. This will come in future revisions of the library if so. What about the other SPI/USART pins On most ...