It has not been necessary to include dependencies of libraries in the sketch since Arduino IDE 1.6.5 and that (and previous) IDE version did not contain the Mouse or HID libraries since their functions were part of the core so I don't think there is any need for this sentence in the readme.
It has not been necessary to include dependencies of libraries in the sketch since Arduino IDE 1.6.5 and that (and previous) IDE version did not contain the Mouse or HID libraries since their functions were part of the core so I don't think there is any need for this sentence in the readme.
Reference: https://github.com/arduino-libraries/Mouse/pull/5