Clarify create_with_advisory_lock usage

Explain how it mainly relates to transactions and the visibility of new records.

lib/good_job/lockable.rb

@@ -87,8 +87,15 @@ module Lockable
 
  # @!attribute [r] create_with_advisory_lock
  # @return [Boolean]
- # Whether an advisory lock should be acquired immediately after creating
- # the record.
+ # Whether an advisory lock should be acquired in the same transaction
+ # that created the record.
+ #
+ # This helps prevent another thread or database session from acquiring a
+ # lock on the record between the time you create it and the time you
+ # request a lock, since other sessions will not be able to see the new
+ # record until the transaction that creates it is completed (at which
+ # point you have already acquired the lock).
+ #
  # @example
  # record = MyLockableRecord.create(create_with_advisory_lock: true)
  # record.advisory_locked?