Add agent-shell-queue-transient link to README

[mrcnski]

See the repo at https://github.com/mrcnski/agent-shell-queue-transient. I'm dogfooding it and finding the interface to be quite handy.

Checklist

• I agree to communicate (PR description and comments) with the author myself (not AI-generated).
• I've reviewed all code in PR myself and will vouch for its quality.
• I've read and followed the Contributing guidelines.
• I've filed a feature request/discussion for a new feature.
• I'm making visual changes, so I'm including screenshots so you can view and discuss.
• I've added tests where applicable.
• I've updated documentation where necessary.
• I've run M-x checkdoc and M-x byte-compile-file.

[xenodium]

Getting 404. Is the repo private?

[mrcnski]

Just made it public, thanks!

[xenodium]

I can access now. Merged!