update current reading note

unlike pololu/dual-vnh5019-motor-shield we include ATmega1280, and ATmega2560 in the note for this library

README.md

@@ -149,7 +149,7 @@ Returns 1 if there is a fault on motor driver 4, 0 if no fault.
 ### Current readings
 
 The current readings returned by `getM1CurrentMilliamps`, `getM2CurrentMilliamps`, `getM3CurrentMilliamps` and
-`getM4CurrentMilliamps` will be noisy and unreliable if you are using a PWM frequency below about 5 kHz.  We expect these readings to work fine if you are using a board based on the ATmega168, ATmega328P, or ATmega32U4, since this library uses 20 kHz hardware PWM on those boards.
+`getM4CurrentMilliamps` will be noisy and unreliable if you are using a PWM frequency below about 5 kHz.  We expect these readings to work fine if you haven't remapped the PWM pins and you are using a board based on the ATmega168, ATmega328P, ATmega328PB, ATmega32U4, ATmega1280, or ATmega2560 since this library uses 20 kHz hardware PWM on those boards.
 
 On other boards, this library uses `analogWrite` to generate PWM signals, which usually means that the PWM frequency will be too low to
 get reliable current measurements.  If `analogWrite` uses a frequency of 490 Hz or more on your board, you can add a 1 µF (or larger) capacitor between each current sense line you are using and GND.  To make `getM1CurrentMilliamps` work well, you would add the capacitor between M1CS and GND.  To make `getM2CurrentMilliamps` work well, you would add the capacitor between M2CS and GND.