release note for v3.0beta2
update release note
Merge pull request #120 from minggo/release-beta2

release note for v3.0beta2
issue #3852:Add a document to describe how to use ZeroBrane Studio to debug lua code
Merge branch 'master' of https://github.com/cocos2d/cocos-docs into luaDocument
Merge pull request #121 from samuele3hu/luaDocument

issue #3852:Modify some description
Merge branch 'master' of https://github.com/cocos2d/cocos-docs