flake: Introduce pytec to PYTHONPATH in devShell

For easier testing of pytec client code in the shell.

flake.nix

@@ -67,6 +67,9 @@
           ] ++ (with python3Packages; [
             numpy matplotlib
           ]);
+        shellHook = ''
+          export PYTHONPATH=`pwd`/pytec:$PYTHONPATH
+        '';
       };
     };
 }