The Release Notes (RNs) are provided as a read-only Tinderbox TBX file and are accessed via the Help menu. The document can help users finding out about minor fixes, improvements and additions for each release that don't necessarily rate mentioning in the manual. The RNs form much of the initial input to ongoing changes in aTbRef.
As the RNs are constantly updated during development so are up to date when a new Tinderbox version is released. Thus at release they can contain information not yet added to the formal manual. Given that the RNs are primarily written as a reference of changes/additions for staff and testers and as such aren't formatted or checked for typos, etc., nor are they written as detail instructions for inexperienced users. They are most likely to be of use as a reference for experienced users. Nonetheless, they are still always available to all users via the Help menu.
Although the RNs are stored in the application package, it is possible to extract a copy.
When the the RNs are opened from the Help menu, note that the contents can't be edited or altered - this includes copying note content. However, though you can't select text in a read-only note in the normal drag-select manner. Instead, either Cmd+drag a selection or use Cmd+A to select all the note's text. Then use Cmd+C to copy it. Alternatively, if doing a lot of copying, consider copying the RNs TBX to a location outside Tinderbox from where you will have normal edit controls (see link above).