kiji-scoring: SCORE-33. Improve InternalFreshKijiTableReader top level JavaDoc

issue: https://jira.kiji.org/browse/SCORE-33
review: https://review.kiji.org/r/1225
commit: https://github.com/kijiproject/kiji-scoring/commit/4e1a0087b53efcaa9d6ea47236c4a309678d8553