Some language and formatting tweaks for the readme,

hopefully making some of the long drawn out sentences easier to understand.

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73978 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Floatcanvas docs and test updates from Werner

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73979 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Use an existing bitmap file so tests will pass

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73980 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775