(minor) dependency: libi2c-dev required to build

[timburks]

If running make produces the following error,

$ make
cc ./raspberrypi-fast-ts.c -O2 -o ./raspberrypi-fast-ts
./raspberrypi-fast-ts.c:17:10: fatal error: i2c/smbus.h: No such file or directory
 #include <i2c/smbus.h>

this can be fixed with sudo apt-get install libi2c-dev

[ardera]

Thanks!

I think I can get it working without libi2c-dev. (Actually, I thought I was only using linux kernel headers in the first place) If that doesn't work I'll add that dependency to the readme