code: func (q *Query) Comment(comment string) *Query {
  	q.m.Lock()
  	q.op.options.Comment = comment
  	q.op.hasOptions = true
  	q.m.Unlock()
  	return q
  }
docs: // Comment adds a comment to the query to identify it in the database profiler output.
  //
  // Relevant documentation:
  //
  //     http://docs.mongodb.org/manual/reference/operator/meta/comment
  //     http://docs.mongodb.org/manual/reference/command/profile
  //     http://docs.mongodb.org/manual/administration/analyzing-mongodb-performance/#database-profiling
  //