auto-multiple-choice: add itself to PATH in the wrapper

auto-multiple-choice (the GUI) needs to run subcommands of itself,
e.g., `auto-multiple-choice prepare ...` to work correctly. Until now,
for this to work, it was necessary to install auto-multiple-choice to
$PATH. Running it via e.g. `nix run` was not possible.

This commit changes that. It enables not only using `nix run`, but
also having multiple working AMC versions installed simultaneously.

pkgs/applications/misc/auto-multiple-choice/default.nix

@@ -90,6 +90,7 @@ stdenv.mkDerivation (finalAttrs: rec {
       XMLWriter
     ]}:"$out/share/perl5 \
     --prefix XDG_DATA_DIRS : "$out/share:$XDG_ICON_DIRS:$GSETTINGS_SCHEMAS_PATH" \
+    --prefix PATH : "$out/bin" \
     --set TEXINPUTS ":.:$out/tex/latex"
   '';