kijiproject.github.com: SCORE-138. Add KijiScoring Userguide.

issue: https://jira.kiji.org/browse/SCORE-138
review: https://review.kiji.org/r/1421
commit: https://github.com/kijiproject/kijiproject.github.com/commit/3273ffc1b08d8bb983b45c9e02fb4cfb27c642c9