Update README to mention Bootstrap 3
Update README to mention Bootstrap 3

See #24

salcode/bootstrap-genesis,michaelcarwile/bootstrap-genesis,bryanwillis/bootstrap-genesis,bryanwillis/bootstrap-genesis,michaelcarwile/bootstrap-genesis,michaelcarwile/bootstrap-genesis,salcode/bootstrap-genesis,bryanwillis/bootstrap-genesis,salcode/bootstrap-genesis