To support similar looking github pages across all my repos (if I so choose) I
submodule this as the _layouts
folder.
$ git submodule add git@github.com:natronics/jekyll-layouts.git _layouts
$ git commit -m "adding jekyll layout submodule"
$ git submodule init
$ cd _layouts
$ git checkout master
$ git pull
$ git commit -am "Pulled down update to submodule_dir"