Here are the new fields for the instrument entity:

name (maps to instrument.name in SQL)
comment (maps to instrument.comment)
type (maps to instrument.type which joins on instrument_type.id to get instrument_type.name)
description (maps to instrument.description)

Instruments also have aliases and annotations like other entities.

Here's the schema referenced above:
https://bitbucket.org/metabrainz/musicbrainz-server/src/schema-change-2014-05/admin/sql/updates/20140214-add-instruments.sql?at=schema-change-2014-05