provide a binary cache for anyrun (#39)

* upload built binaries to cachix

* add cachix instructions to the README

.github/workflows/cachix.yml

@@ -0,0 +1,45 @@
+name: "Set up binary cache & push binaries"
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+    paths-ignore:
+      - .github/**
+      - assets/**
+      - .gitignore
+
+jobs:
+  cahix:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        package:
+          - default
+    steps:
+      - uses: easimon/maximize-build-space@v6
+        with:
+          overprovision-lvm: true
+          remove-android: true
+          remove-dotnet: true
+          remove-haskell: true
+      - uses: actions/checkout@v3
+      - uses: cachix/install-nix-action@v20
+        with:
+          extra_nix_config: |
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+            auto-optimise-store = true
+            experimental-features = nix-command flakes
+          nix_path: nixpkgs=channel:nixos-unstable
+      - uses: cachix/cachix-action@v12
+        with:
+          authToken: ${{ secrets.CACHIX_TOKEN }}
+          extraPullNames: nix-community
+          name: anyrun
+      - name: Set default git branch (to reduce log spam)
+        run: git config --global init.defaultBranch main
+      - name: Validate Flakes
+        run: nix flake check
+      - name: Build anyrun with default settings
+        run: nix build .#${{ matrix.package }} --print-build-logs