chore: add examples for flake-parts and rensa-nix

examples/rensa-nix/flake.nix

@@ -0,0 +1,30 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    ren.url = "gitlab:rensa-nix/core?dir=lib";
+  };
+
+  outputs = {
+    self,
+    ren,
+    ...
+  } @ inputs:
+    ren.buildWith
+    {
+      inherit inputs;
+      cellsFrom = ./nix;
+      transformInputs = system: i:
+        i
+        // {
+          pkgs = import i.nixpkgs {inherit system;};
+        };
+      cellBlocks = with ren.blocks; [
+        (simple "ci")
+      ];
+    }
+    {
+      packages = ren.select self [
+        ["repo" "ci" "packages"]
+      ];
+    };
+}