configuration for ProofGeneral with a Dune build of UniMath and this satellite

[rmatthes]

The present issue is perfectly analogous to UniMath/GrpdHITs#28 .

Analogous to the suggested solution for that issue, the file name below has been suffixed with .txt so as to be acceptable as an attachment to this issue. The renamed file should be put into the already existing directory code

.dir-locals.el.txt

.