build: add nix flake & nix install step

.github/workflows/build-release.yml

@@ -18,6 +18,9 @@ jobs:
         with:
           repository: holochain/holochain
           ref: ${{ github.event.client_payload.ref }}
+      - uses: cachix/install-nix-action@v22
+        with:
+          github_access_token: ${{ secrets.GITHUB_TOKEN }}
       - name: "Build"
         env:
           system: ${{ matrix.platform.system }}

flake.nix

@@ -0,0 +1,36 @@
+{
+  description = "Template for Holochain app development";
+
+  inputs = {
+    versions.url  = "github:holochain/holochain?dir=versions/0_2";
+
+    holochain-flake.url = "github:holochain/holochain";
+    holochain-flake.inputs.versions.follows = "versions";
+
+    nixpkgs.follows = "holochain-flake/nixpkgs";
+    flake-parts.follows = "holochain-flake/flake-parts";
+  };
+
+  outputs = inputs:
+    inputs.flake-parts.lib.mkFlake
+      {
+        inherit inputs;
+      }
+      {
+        systems = builtins.attrNames inputs.holochain-flake.devShells;
+        perSystem =
+          { inputs'
+          , config
+          , pkgs
+          , system
+          , ...
+          }: {
+            devShells.default = pkgs.mkShell {
+              inputsFrom = [ inputs'.holochain-flake.devShells.holonix ];
+              packages = [
+                pkgs.nodejs-18_x
+              ];
+            };
+          };
+      };
+}