add(nix): add binary cache zellij (#1157)

adds a binary cache called `zellij`, hosted by
https://www.cachix.org/
to the project, users can now use the cache by running:
```
cachix use zellij
```

Step by step:
```
bash <(curl -L https://nixos.org/nix/install)
nix-env -iA cachix -f https://cachix.org/api/v1/install
cachix use zellij
nix-build
```

Documentation: https://docs.cachix.org/installation#

.github/workflows/nix.yml

@@ -12,6 +12,7 @@ jobs:
   nix:
     runs-on: ubuntu-latest
     name: nix-build
+    environment: cachix
     timeout-minutes: 15
     steps:
       - uses: actions/checkout@v2.4.0
@@ -23,5 +24,11 @@ jobs:
           extra_nix_config: |
             experimental-features = nix-command flakes
           fetch-depth: 0
+      - uses: cachix/cachix-action@v10
+        with:
+          name: zellij
+          # If you chose API tokens for write access OR if you have a private cache
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
       - run: nix flake check --print-build-logs --show-trace
       - run: nix build
+      - run: nix develop --profile devShell

flake.nix

@@ -67,6 +67,8 @@
             pkgs.nixpkgs-fmt
             # optimizes wasm binaries
             pkgs.binaryen
+
+            pkgs.jq
           ];
 
         in