Add psq 0.2.1

[robhoes]

No description provided.

[duobei]

I'm curious how checksum is generated, is it automatic or do we generate it manually?
And how does x-commit-hash come about?

[edwintorok]

I think this is done automatically by opam. In this case this file is a copy of the file from the upstream repo.

[robhoes]

Yes, all I did to create this opam file was the following:

opam show psq.0.2.1 --raw > packages/upstream/psq.0.2.1/opam

[edwintorok]

And 'x-commit-hash' is added by dune itself when making a release, so you know which commit the release was made from.