[doc]Add dev/user readme
[usecase-wrt]Add Readme file
[usecase-cordova] Add README.md for cordova usecase
[wrt-usecase] Add readme files to subcase
Merge pull request #987 from linshen/shenlin/usrcase/add_readme

[usecase-wrt]Add Readme file
Merge pull request #983 from wanghongjuan/wanghongjuan/usecase/readme

[wrt-usecase] Add readme files to subcase
Merge pull request #982 from haoxli/haoxli/usecase/cordova-readme

[usecase-cordova] Add README.md for cordova usecase
Merge pull request #988 from linshen/shenlin/adddocreadme

[doc]Add WRT dev/user readme