data.md: wrong braincloud link
Merge pull request #4 from kbroman/fix_braincloud_link

data.md: wrong braincloud link
Remove _site dir

 - Also added .gitignore file with "_site"

 - _site is built when you push to github, so you don't need to include
   it in the repo
Merge pull request #5 from kbroman/remove_site_dir

Remove _site dir