Add GitHub actions (#8)

Author: ocharles

.github/workflows/build.yaml

@@ -0,0 +1,16 @@
+name: Build
+on: [push, pull_request, release]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/[email protected]
+      with:
+          persist-credentials: false
+          submodules: true
+
+    - uses: cachix/install-nix-action@v12
+      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/"