Added usage example

README.md

@@ -0,0 +1,37 @@
+# Usage
+
+Based on [the-nix-way](https://github.com/the-nix-way/dev-templates)
+
+```flake.nix
+{
+  description = "A Nix-flake-based R development environment";
+
+  inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1";
+  inputs.fran.url = "github:dwinkler1/fran";
+  inputs.fran.inputs.nixpkgs.follows = "nixpkgs";
+
+  outputs = inputs: let
+    supportedSystems = ["x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin"];
+    forEachSupportedSystem = f:
+      inputs.nixpkgs.lib.genAttrs supportedSystems (system:
+        f {
+          pkgs = import inputs.nixpkgs {
+            inherit system;
+            overlays = [inputs.fran.overlays.default];
+          };
+        });
+    mkR = inputs.fran.lib.mkR;
+  in {
+    devShells = forEachSupportedSystem ({pkgs}: {
+      default = pkgs.mkShell {
+        packages = with pkgs; [
+          (mkR {
+            inherit pkgs;
+            packages = [rPackages.data_table extraRPackages.fwildclusterboot];
+          })
+        ];
+      };
+    });
+  };
+}
+```