Add `AGENTS.md` for compatibility with `usage_rules`

[sitch]

Support https://github.com/ash-project/usage_rules by adding an AGENTS.md file at the root of the repo.

Anecdotal issues so far:

Invalid generated claude code:

real_part = Nx.real(field) |> Nx.reshape({1, 1} ++ Tuple.to_list(Nx.shape(field)))
imag_part = Nx.imag(field) |> Nx.reshape({1, 1} ++ Tuple.to_list(Nx.shape(field)))

Although this is technically more of a Tuple issue where Kernel.++/2 is only implemented for lists, instructing the LLM to construct complex shapes with build_list |> Tuple.from_list() |> Nx.reshape()

[sitch]

Some guidance around callers within defn would be useful as well

i.e.:

** (CompileError) lib/example/example.ex:711 Nx.to_number/1 is not allowed inside defn

[polvalente]

A PR is welcome! We can iterate on it more easily from there.

The ++ issue is definitely not Nx-specific, but having an example on how to add leading axes should be useful. Especially one like the one you provided inside a defn, where deftransform would be required.

[polvalente]

One question: for monorepos like this, I assume the AGENTS.md file would be at the root of each lib, not the repo, right?

[josevalim]

Yes, it looks up based on the Hex package, so it needs to be per folder and you need to make sure to include it in the package.