Clarify maintainership status

[florisla]

Hi,

It seems this repository receives no maintenance anymore.

I'm glad to assist ; I have a modernized fork at https://github.com/florisla/stm32loader . I'd be open for all options - merge back to here, put this repository under an organization, ...

Please weigh in on how you'd like stm32loader to evolve.

The current situation is confusing for users, since there's no indication that merge requests are not being considered. See e.g. https://github.com/jsnyder/stm32loader/pull/16#issuecomment-537886550