add new tutorial about android，part 1. introduction.
fixed #3343, add source code for Chapter 5 of Parkour game
add how to use jni.
Merge branch 'master' of https://github.com/cocos2d/cocos-docs
add how to use jnihelper and screenshot.
Merge branch 'master' of https://github.com/cocos2d/cocos-docs
Merge pull request #59 from u0u0/master

fixed #3343, add source code for Chapter 5 of Parkour game
change folder name.
Merge branch 'master' of https://github.com/cocos2d/cocos-docs