Move most of SETUP.md to getting started with C++ page
Move most of SETUP.md to getting started with C++ page

patricksjackson/xcpp,daniellehrner/xcpp,daniellehrner/xcpp,NobbZ/xcpp,patricksjackson/xcpp,lukasz-m-maciejewski/xcpp,exercism/xcpp,NobbZ/xcpp,oalbe/xcpp,exercism/xcpp,oalbe/xcpp,lukasz-m-maciejewski/xcpp