Add Cachix (#14)

Author: ocharles

.github/workflows/build.yaml

@@ -13,4 +13,9 @@ jobs:
       with:
         nix_path: nixpkgs=channel:nixos-unstable
 
-    - run: nix-build -A hsPkgs.dear-imgui.components.exes --option trusted-public-keys "hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= iohk.cachix.org-1:DpRUyj7h7V830dp/i6Nti+NEO2/nhblbov/8MW7Rqoo= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=" --option substituters "https://hydra.iohk.io https://iohk.cachix.org https://cache.nixos.org/"
+    - uses: cachix/cachix-action@v8
+      with:
+        name: hs-dear-imgui
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+
+    - run: nix-build -A hsPkgs.dear-imgui.components.exes