Add Android Camera To Unity Plugin

webrtc/examples/unityplugin/README

-This directory contains an example Unity native plugin for Windows OS.
+This directory contains an example Unity native plugin for Windows OS and Android.
+
 The APIs use Platform Invoke (P/Invoke) technology as required by Unity native plugin.
 This plugin dll can also be used by Windows C# applications other than Unity.
 
+For detailed build instruction on Android, see ANDROID_INSTRUCTION
+
 An example of wrapping native plugin into a C# managed class in Unity is given as following:
 
 using System;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
 
 namespace SimplePeerConnectionM {
   // A class for ice candidate.
   public class IceCandidate {
     public IceCandidate(string candidate, int sdpMlineIndex, string sdpMid) {
@@ skipping 282 matching lines @@
 
     private LocalSdpReadytoSendInternalDelegate localSdpReadytoSendDelegate = null;
     public event LocalSdpReadytoSendDelegate OnLocalSdpReadytoSend;
 
     private IceCandiateReadytoSendInternalDelegate iceCandiateReadytoSendDelegate = null;
     public event IceCandiateReadytoSendDelegate OnIceCandiateReadytoSend;
 
     private int mPeerConnectionId = -1;
   }
 }