Add screenshots to readme.
Add screenshots to readme.

Let knew users know what it'll look like.

ansiz/goconvey,yaoshipu/goconvey,aquilax/goconvey,ansiz/goconvey,yaoshipu/goconvey,aquilax/goconvey,wallclockbuilder/goconvey,wallclockbuilder/goconvey,yaoshipu/goconvey,wallclockbuilder/convey,ansiz/goconvey,wallclockbuilder/goconvey,aquilax/goconvey