fix requested changes by @aykevl

i2c.go

@@ -3,7 +3,15 @@ package drivers
 // I2C represents an I2C bus. It is notably implemented by the
 // machine.I2C type.
 type I2C interface {
-	// ReadRegister(addr uint8, r uint8, buf []byte) error
-	// WriteRegister(addr uint8, r uint8, buf []byte) error
+	// Tx performs a [I²C] transaction with address addr.
+	// Most I2C peripherals have some sort of register mapping scheme to allow
+	// users to interact with them:
+	//
+	//  bus.Tx(addr, []byte{reg}, buf) // Reads register reg into buf.
+	//  bus.Tx(addr, append([]byte{reg}, buf...), nil) // Writes buf into register reg.
+	//
+	// The semantics of most I2C transactions require that the w write buffer be non-empty.
+	//
+	// [I²C]: https://en.wikipedia.org/wiki/I%C2%B2C
 	Tx(addr uint16, w, r []byte) error
 }