Unclear README regarding usage of binary caches

[DamienCassou]

Hi,

after reading the README, I'm unsure if (1) nix-index actually searches binary caches on the web or (2) only the /nix/store directory locally.

In favor of the first (remote) interpretation, I read

It indexes built derivations found in binary caches.

In favor of the second (local) interpretation, I read

• all lines in nix-locate contains /nix/store
• no sentence indicates which external binary cache is contacted, nor how to configure that (if at all possible) or even how the tools does it.

I think the README could be clarified so the reader isn't confused.

[bennofs]

To answer your question: it uses cache.nixos.org, the default nixos/nix binary cache. Configuring it is not possible right now.

I'll look into clarifying the readme.