add docs about 3D audio

content/Audio/_index.md

@@ -46,3 +46,25 @@ jumpSoundEffectInstance.Pitch = -0.25f;
 jumpSoundEffectInstance.Pan = -0.5f;
 jumpSoundEffectInstance.Play();
 ```
+
+### 3D Audio
+
+MoonWorks has support for 3-dimensional audio.
+To use it, you must create an AudioListener, and any sounds that are emitted in 3-dimensional space should use an AudioEmitter.
+Emitters and listeners use position, orientation, and velocity to determine audio playback.
+Then you can call `Apply3D` on a sound effect instance and provide the emitter and listener.
+
+```cs
+var audioEmitter = new AudioEmitter(AudioDevice);
+var audioListener = new AudioListener(AudioDevice);
+
+audioEmitter.Position = thingPosition;
+audioEmitter.Forward = thingForward;
+audioEmitter.Up = thingUp;
+
+audioListener.Position = cameraPosition;
+audioListener.Forward = cameraForward;
+audioListener.Up = cameraUp;
+
+thingSound.Apply3D(audioListener, audioEmitter);
+```