Lower default SPI clock speed

- Testing with TCP/IP (RF24Ethernet and RF24toTUN) indicates a need for
lower SPI clock rates to reduce errors and/or hangs
Merge remote-tracking branch 'origin/master' into Updates
Enable hardware warnings by default on linux

- Enable warnings by default on linux if the radio is not responding
- Revert reduction in SPI speed pending further testing
Update python readme and example

- Added more detailed setup information
- Clarified the user config portion of the example python sketch per #49
Attempt to correct markdown formatting in readme
Attempt 2 to fix python readme formatting