nodePackages.purs-tidy: add meta.mainProgram (#247768)

Changed files
+1
pkgs
development
node-packages
+1
pkgs/development/node-packages/main-programs.nix
···
postcss-cli = "postcss";
prettier = "prettier";
purescript-psa = "psa";
+
purs-tidy = "purs-tidy";
react-native-cli = "react-native";
react-tools = "jsx";
remod-cli = "remod";