Fix links to informal quint #269
Description
The CI reports the following dead links:
[✖] https://github.com/informalsystems/quint/blob/main/tutorials/README.md → Status: 404
[✖] https://github.com/informalsystems/quint/blob/main/doc/quint-cheatsheet.pdf → Status: 404
[✖] https://github.com/informalsystems/quint/blob/main/doc/builtin.md → Status: 404