Update README.md

README.md

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 Simple monitor for displaying MIDI status for digital pianos.
 
+Supports a keyboard span of 9 octaves (C0-B8, MIDI note number 12-119), as well as
+pedal status for soft pedal/una corda (MIDI CC number 67, binary switch: 0-63 is off,
+64-127 is on), sostenuto (MIDI CC number 66, binary switch: 0-63 is off, 64-127 is on),
+and sustain (MIDI CC number 64, values from 0-127).
+
 ![Screenshot](./docs/screenshot.png)
 
 Tested with Node v.14.1.0