kiji-express: DOCS-107. API doc for KijiInput needs to include the syntax required to use the object

issue: https://jira.kiji.org/browse/DOCS-107
review: https://review.kiji.org/r/1230
commit: https://github.com/kijiproject/kiji-express/commit/010fb7e0a4c231a5db1cc65fdb6ff127772c6b4b