Add the libraries for undecidability and first-order logic to the Platform about platform

[yforster]

Thanks for bringing this up Karl, I'm in favour of including both!

I just prepared for an opam release compatible with 8.18 for coq-library-undecidability, @dominik-kirst and @JoJoDeveloping will soon do the same for coq-library-fol.

In the line of basic computer science concepts there is also https://github.com/uds-psl/coq-library-complexity with the Cook-Levin theorem and a time equivalence proof for Turing machines and lambda-calculus, but it's (probably) forever stuck on 8.16 due to a lack of maintainers.

[yforster]

I've filed coq-community/manifesto#150 for coq-library-complexity to look for a new maintainer, maybe we get lucky :)

[yforster]

There is a release for coq-library-fol now. Is there anything else we need to do for both libraries to be included in the platform? CC @dominik-kirst

[palmskog]

From my perspective, everything technically required is there, hopefully we can hear from the editorial board on a decision soon akin to here, cc @ybertot

I also hope we can get #344 resolved, since coq-library-undecidability depends on it.