kijiproject.github.com: DOCS-153. Music Tutorial and Phonebook Tutorial both have confusing setup instructions

Replace incomlete bento start instructions
with the clear wording in the express tutorial.

review: https://review.kiji.org/r/1633
issue: https://jira.kiji.org/DOCS-153
commit: https://github.com/kijiproject/kijiproject.github.com/commit/d80fa3c1a9430fc36c6ae1d21a022474cea538b1