Update readme to refer to Twenty Twenty-Four

[karmatosed]

We have a newer default theme and with that my recommendation would be that the readme here is updated.

There are a few things I would recommend for the readme and perhaps approaches here:

• Consider if child themes is the right approach of TT3 or TT4, or if it could use 'Create Block plugin'.
• If it does use child themes update to TT4.

This would involve updating the readme documentation.

[MaggieCabrera]

Are you thinking of something specific? Please feel free to suggest the changes where you see it fit