nix: nix-buildable figures

default.nix

@@ -13,6 +13,19 @@ let
         pdftk
       ];
     };
+    figures = pkgs.stdenv.mkDerivation {
+      name = "figures";
+      buildInputs = shell.buildInputs;
+      src = pkgs.lib.sourceByRegex ./. [
+        "build\.ninja"
+        "fig"
+        "fig/.*\.svg"
+      ];
+      installPhase = ''
+        mkdir -p $out
+        cp pipe-usage-example.pdf $out/
+      '';
+    };
   };
 in
   self