[3.1 release] Improve Facebook Integration documents
[Cocos2d-JS] Improve docs for 3.1 release and Facebook sdk
Merge branch 'master' of https://github.com/cocos2d/cocos-docs
Merge pull request #561 from pandamicro/master

[Cocos2d-JS] Improve docs for 3.1 release and Facebook docs
improve facebook documentation