Added instructions about building applications using wxMSW.

Added instructions about building applications using wxMSW.

Explaining how to build wxWidgets itself is insufficient as usually people
want to actually build their programs using it and not just the library
itself, so add a section explaining how to build the projects using wxMSW.

Also add a table of contents and mention that MSVC and g++ are the main
supported compilers.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69858 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775