Add nix shell

shell.nix

@@ -0,0 +1,29 @@
+{ pkgs ? import <nixpkgs> {} }:
+let
+  sp-python = pkgs.python39.withPackages (p: with p; [
+    flask 
+    flask-restful 
+    setuptools 
+    portalocker 
+    flask-swagger 
+    flask-swagger-ui 
+    pytz 
+    pytest 
+    pytest-mock 
+    pytest-datadir 
+    huey 
+    gevent
+    mnemonic
+    coverage
+  ]);
+in
+pkgs.mkShell {
+  buildInputs = [
+    sp-python
+    pkgs.black
+  ];
+  shellHook = ''
+    PYTHONPATH=${sp-python}/${sp-python.sitePackages}
+    # maybe set more env-vars
+  '';
+}