Add Nix CI workflow, update docs and cargo hash

.gitea/workflows/nix.yml

@@ -0,0 +1,23 @@
+name: Nix package
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container: node:22-bookworm
+    steps:
+      - name: Checkout
+        uses: https://github.com/actions/checkout@v4
+      - name: Install runner prerequisites
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends sudo
+      - name: Install Nix
+        uses: https://github.com/cachix/install-nix-action@v31
+        with:
+          enable_kvm: false
+      - name: Build default.nix package
+        run: nix build .#default --no-update-lock-file --no-link --print-out-paths --print-build-logs