Add badge, wiki link and dev guide

README.md

@@ -1,5 +1,25 @@
 # v2rayNG
 
+A V2Ray client for Android
+
+[![API](https://img.shields.io/badge/API-17%2B-yellow.svg?style=flat)](https://developer.android.com/about/versions/jelly-bean#android-4.2)
+[![Kotlin Version](https://img.shields.io/badge/Kotlin-1.3.40-blue.svg)](https://kotlinlang.org)
+[![GitHub commit activity](https://img.shields.io/github/commit-activity/m/2dust/v2rayNG)](https://github.com/2dust/v2rayNG/commits/master)
+[![CodeFactor](https://www.codefactor.io/repository/github/2dust/v2rayng/badge)](https://www.codefactor.io/repository/github/2dust/v2rayng)
+[![GitHub Releases](https://img.shields.io/github/downloads/2dust/v2rayNG/latest/total?logo=github)](https://github.com/2dust/v2rayNG/releases)
+
 <a href="https://play.google.com/store/apps/details?id=com.v2ray.ang">
 <img alt="Get it on Google Play" src="https://play.google.com/intl/en_us/badges/images/generic/en_badge_web_generic.png" width="165" height="64" />
 </a>
+
+### Usage
+
+See our [wiki](https://github.com/2dust/v2rayNG/wiki)
+
+### Development guide
+
+Android project under V2rayNG folder can be compiled directly in Android Studio, or using Gradle wrapper. But the v2ray core inside the aar is (probably) outdated.  
+The aar can be compiled from the Golang project under AndroidLibV2rayLite folder. For a quick start, read guide for [Go Mobile](https://github.com/golang/go/wiki/Mobile)
+and [Makefiles for Go Developers](https://tutorialedge.net/golang/makefiles-for-go-developers/)
+
+v2rayNG can run on Android Emulators, with minimum Android 5.0