There's a library A in Rust that's not being updated on crates.io, but only at github. There's another repo into which I want to add a bagde-tags, into README.md, which will show the current version of the A and do so dynamically. I'm aware of shields.io and similar things but how to make them to determine the version of A dynamically?
If this “library A” has tags for its versions on github then something like
https://img.shields.io/github/v/release/USER/REPO?label=LABEL&sort=semver
could work for you.
for example
https://img.shields.io/github/v/release/serde-rs/serde?label=serde&sort=semver
Also, you do emphasize the word “dynamically” a lot without explaining what exactly you mean, but also mention you know about shields.io, so I’m not 100% sure this is what you were asking for.