Update README.md

Author: ricardoquesada

README.md

@@ -1,4 +1,8 @@
 cocos2d-x-dependencies
 ======================
 
-Dependencies of cocos2d-x.
+This repository includes the source code of the binary libraries that are bundled with cocos2d-x.
+
+This repository is only needed for cocos2d-x developers or people who want to port cocos2d-x to other platforms.
+
+As an example, if you want to support cocos2d-x in ARM64, you need to compile all these libraries for ARM64.