add breadcrumbs if possible

[dmalan]

• https://github.com/git-no/jekyll-breadcrumbs
• https://stackoverflow.com/questions/9612235/what-are-some-good-ways-to-implement-breadcrumbs-on-a-jekyll-site
• https://gist.github.com/csgruenebe/8f7beef9858c1b8625d6
  • https://gist.github.com/dhhepting/877cd31b7f9ead5c0eb88bcb1a982adf