Move most of SETUP.md to getting started with C++ page.
Add C++ metadata, fix sort order.

Change the sort order to follow ASCII ordering (# before +, #/+ before A),
and change the sort ordinals so that there is room between sort ordinals
allowing a new language to be inserted, just like renumbering line numbers
in BASIC.
Add language about single source file submission
Merge pull request #50 from LegalizeAdulthood/getting-started-with-cpp

Getting started with cpp