Update README.md

Author: avandalen

README.md

@@ -1 +1,7 @@
-# avdweb_AnalogReadFast
+### avdweb_AnalogReadFast
+The standard Arduino analogRead() takes about 112us for the AVR and 425us for the SAMD21, this is very slow. 
+The new function analogReadFast() takes just 21us. 
+Compatible with
+- AVR boards: Arduino Uno, Nano, Mega, Leonardo, etc.
+- SAMD21 boards: Arduino Zero, SAM 15x15, etc. 
+http://www.avdweb.nl/arduino/libraries/fast-10-bit-adc.html