[WEEX-473][doc] Update HOW-TO-BUILD.md for weexcore
diff --git a/HOW-TO-BUILD.md b/HOW-TO-BUILD.md
index 40a548a..0cfc0ea 100644
--- a/HOW-TO-BUILD.md
+++ b/HOW-TO-BUILD.md
@@ -17,6 +17,8 @@
* Android SDK(`$ANDROID_HOME` must be set properly)
* Android NDK(version <= 16, `$ANDROID_NDK` must be set properly)
* Gradle 2.0+
+ * NDK r16
+ * CMake 3.9.0+
* iOS SDK:
* NodeJS 4.0+
* XCode & Command Tools 8.0+
diff --git a/README.md b/README.md
index c51287a..d6204d9 100644
--- a/README.md
+++ b/README.md
@@ -37,6 +37,8 @@
* `npm install`, install project
* `./start`
* Install [Android Environment](http://developer.android.com/training/basics/firstapp/index.html)
+ * Install [NDK](https://developer.android.com/ndk/) r16
+ * Install [Cmake](https://cmake.org/download/) 3.9.0+
* Run playground, In Android Studio
* Open `android/playground`
* In `app/java/com.alibaba.weex/IndexActivity`, modify `CURRENT_IP` to your local IP
