flake: add devShells

exposed via nix registry :D
can be used in nix-direnv like `use flake shells#cs.osu`

shells/php/osu-web.nix

@@ -0,0 +1,26 @@
+# Flake for development on https://github.com/ppy/osu-web
+{
+  mkShell,
+  nodejs-14_x,
+  nodePackages,
+  php80,
+  php80Packages,
+  python3
+}:
+let
+  phpPkg = php80.withExtensions ({ enabled, all }:
+    enabled ++ [ all.intl all.redis ]
+  );
+in mkShell {
+  buildInputs = [
+    nodejs-14_x
+    nodePackages.yarn
+    phpPkg
+    php80Packages.composer
+    python3
+  ];
+
+  shellHook = ''
+    export PATH="$(readlink -f ./node_modules/.bin):$PATH"
+  '';
+}