Update README.adoc

added digital potentiometer control functions for amplifier volume

README.adoc

@@ -15,8 +15,11 @@ Compatible with Atmel SAMD series MCU and is best used with DAC related amplifie
         // change the state of the shutdown pin of an amplifier while setting mute flag
 
     void selectDACPin(uint8_t audioOutputPin);
-        // select the audio output pin on the microcontroller
+        // select the audio output pin on the microcontroller4
 
+    void selectDigitalPotPin(uint8_t DigitalPotPin);
+        // select the digital potentiometer pin on the microcontroller
+
     setBlocking(bool blockFlag);
         // enable or disable blocking mode to prevent code execution play() until audio track finishes, disabled by default
 
@@ -46,6 +49,15 @@ Compatible with Atmel SAMD series MCU and is best used with DAC related amplifie
 
     void gainDown();
         // increase volume (shouldn't need if using hardware gain control)
+
+    void setVolume(uint8_t v);
+       // move the wiper of the digital potentiometer to the selected value from 0 to 100 (scaled to 0-255)
+
+    void volumeUp();
+        // decrement the wiper of the digital potentiometer by one
+
+    void volumeDown();
+        // increment the wiper of the digital potentiometer by one
 
     void end();
         // called to manually stop the audio player