Created a basic readme

A blank readme may be overwhelming to new users that are interested in trying out this amazing RepRap controller. I added some basic setup instructions.
Update README.md
Merge pull request #8 from revarbat/master

M28 sdcard capture fix
Merge pull request #9 from revarbat/master

Reformatted output of M503 to be more friendly to cut-and-pasting into a gcode file.
Merge pull request #10 from wildBill83/master

Updated Readme
Update heaters.c

Added mintemp for PID autotune thermistor fault.
Merge pull request #11 from wildBill83/master

PID autotune min temp
Updated no thermistor protection in PIDAT

Fixed the logic, it should not error with a working thermistor now. Also fixed a typo at jglauche's request. :)
Merge pull request #12 from wildBill83/master

Updated heaters.c
Merge branch 'master' of github.com:kliment/4pi-firmware