recommend nix-locate/nix-index

source/tutorials/learning-journey/packaging-existing-software.md

@@ -380,6 +380,8 @@ You can see a few warnings which should be corrected in the upstream code, but t
 
 :::{note}
 Determining from where to source a dependency is currently a somewhat-involved process: it helps to become familiar with searching the `nixpkgs` source for keywords.
+
+Consider using `nix-locate` from the [`nix-index`](https://github.com/nix-community/nix-index) tool to find derivations that provide what you need.
 :::
 
 You will need the `Xlib.h` headers from the `X11` C package, the Nixpkgs derivation for which is `libX11`, available in the `xorg` package set.