Enter post-focus reminder

It might be useful to have the option to leave yourself a reminder for when a focus period ends.

This could probably just be some plain text, but I often find myself clicking through to a new focus period, then shortly after remembering that I meant to take a break to deal with something else.

Might be outside the scope/purpose of Build Focus, but integrating with a todo list or something seems harder than just adding a text note :)