This adds the git headers, so we can easily rebuild a buildroot-for-wrs
tree to add more patches.

This is how I do it now (where "wrs-build" and "wr-switch-sw" are
at the same directory level.

   cd wrs-build

    mkdir tmp; cd tmp
   tar xf ../downloads/buildroot-2016.02.tar.bz2
   cd buildroot-2016.02/

   git init; git add .; git commit -m "buildroot-2016.02 as untarred"
   git am ../../../wr-switch-sw/patches/buildroot/00*
   mv .git ../../build/buildroot-2016.02/

   cd ../../build/buildroot-2016.02
   <work-here>
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>