Add `keywords` to bower.json

See: https://docs.google.com/document/d/1APq7oA9tNao1UYWyOm8dKqlRP2blVkROYLZ2fLIjtWc/edit#heading=h.gexwkmadfy56

http://sindresorhus.com/bower-components/ makes use of the keywords for search.

Not very useful here, but sets a good example for people looking at the jQuery bower.json.