Add dockerfile for android NDK build

android/README.md

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+Copyright (c) 2014-2017, The Monero Project
+
+
+## Current status : ALPHA
+
+ - Minimum Android 5.0 (api level 21)
+ - Modal dialogs can appear in background giving the feeling that the application is frozen (Work around : turn screen off/on or switch to another app and back)
+
+## Build using Docker
+
+# Base environnement
+
+        cd monero/utils/build_scripts
+        docker build -f android32.Dockerfile -t monero-android .
+        cd ..
+
+# Build GUI
+
+        cd android/docker
+        docker build -t monero-gui-android .
+        docker create -it --name monero-gui-android monero-gui-android bash
+
+# Get the apk
+
+        docker cp monero-gui-android:/opt/android/monero-core/build/release/bin/bin/QtApp-debug.apk .
+       
+## Deployment
+
+- Using ADB (Android debugger bridge) : 
+
+  First, see section [Enable adb debugging on your device](https://developer.android.com/studio/command-line/adb.html#Enabling)
+  The only place where we are allowed to play is `/data/local/tmp`. So : 
+
+        adb  push /opt/android/monero-core/build/release/bin/bin/QtApp-debug.apk /data/local/tmp
+        adb  shell pm install -r /data/local/tmp/QtApp-debug.apk
+   
+  - Troubleshooting: 
+  
+        adb devices -l
+        adb logcat
+	
+    if using adb inside docker, make sure you did "docker run -v /dev/bus/usb:/dev/bus/usb --privileged"
+	
+- Using a web server
+
+        mkdir /usr/tmp
+        cp QtApp-debug.apk /usr/tmp
+        docker run -d -v /usr/tmp:/usr/share/nginx/html:ro -p 8080:80 nginx
+
+  Now it should be accessible through a web browser at 
+  
+        http://<your.local.ip>:8080/QtApp-debug.apk
+