Add CI for osx and linux

[goanpeca]

No description provided.

[jakirkham]

Does this mean macOS and Linux are supported (or will be again)? Was a little confused by the note in the README, which made it sound like they are not supported.

[mbargull]

They aren't yet, but @goanpeca wrote down some initial ideas for that in #48.

[github-actions]

Hi there, thank you for your contribution!

This issue has been automatically marked as stale because it has not had recent activity. It will be closed automatically if no further activity occurs.

If you would like this issue to remain open please:

1. Verify that you can still reproduce the issue at hand
2. Comment that the issue is still reproducible and include:
   - What OS and version you reproduced the issue on
   - What steps you followed to reproduce the issue

NOTE: If this issue was closed prematurely, please leave a comment.

Thanks!

[jakirkham]

Presumably we will still want this given there is interest in adding macOS and Linux support ( #48 (comment) )

[jaimergp]

The cep-devel branch has support (and CI) for macOS and Linux. I don't know if we want to close this now or when that branch makes it to main (pending CEP approval).