add rad_development_python to environment and add update instructions

checks.nix

@@ -29,6 +29,7 @@ in
       deadnix = {
         enable = true;
         settings = {
+          exclude = [ "poetry-git-overlay.nix" ];
           noUnderscore = true; # ignore variables starting with underscore
           # ignore lambda patterns (useful for passing args from ({}@args)
           # to other functions)