Submit homebrew formula for libasdf

[embray]

Now that I've learned (just as of today!) that it's possible to run homebrew on Linux, would be good to create a formula specifically for libasdf.

Probably best to wait on that until the 0.1.0 release; then it would make a nice complement to the conda-forge recipe.

[embray]

Worth noting also that homebrew-core has a "notability threshold" for new formulae, which is reasonable: https://github.com/orgs/Homebrew/discussions/6750

But if libasdf doesn't meet the threshold yet I can still make it available via a third-party tap.