Add NixOS integration documentation for updating cm-dashboard

Include step-by-step instructions for updating commit hash and
rebuilding NixOS configuration when new cm-dashboard code is available.

README.md

@@ -446,3 +446,92 @@ MIT License - see LICENSE file for details.
 5. Open Pull Request
 
 For bugs and feature requests, please use GitHub Issues.
+
+## NixOS Integration
+
+### Updating cm-dashboard in NixOS Configuration
+
+When new code is pushed to the cm-dashboard repository, follow these steps to update the NixOS configuration:
+
+#### 1. Get the Latest Commit Hash
+```bash
+# Get the latest commit from the API
+curl -s "https://gitea.cmtec.se/api/v1/repos/cm/cm-dashboard/commits?sha=main&limit=1" | head -20
+
+# Or use git
+git log --oneline -1
+```
+
+#### 2. Update the NixOS Configuration
+Edit `hosts/common/cm-dashboard.nix` and update the `rev` field:
+```nix
+src = pkgs.fetchFromGitea {
+  domain = "gitea.cmtec.se";
+  owner = "cm";
+  repo = "cm-dashboard";
+  rev = "f786d054f2ece80823f85e46933857af96e241b2";  # Update this
+  hash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";  # Reset temporarily
+};
+```
+
+#### 3. Get the Correct Hash
+Build with placeholder hash to get the actual hash:
+```bash
+nix-build --no-out-link -E 'with import <nixpkgs> {}; fetchFromGitea { 
+  domain = "gitea.cmtec.se"; 
+  owner = "cm"; 
+  repo = "cm-dashboard"; 
+  rev = "YOUR_COMMIT_HASH"; 
+  hash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA="; 
+}' 2>&1 | grep "got:"
+```
+
+#### 4. Update the Hash
+Replace the placeholder with the correct hash:
+```nix
+hash = "sha256-vjy+j91iDCHUf0RE43anK4WZ+rKcyohP/3SykwZGof8=";  # Use actual hash
+```
+
+#### 5. Update Cargo Dependencies (if needed)
+If Cargo.lock has changed, you may need to update `cargoHash`:
+```bash
+# Build to get cargo hash error
+nix-build --no-out-link --expr 'with import <nixpkgs> {}; rustPlatform.buildRustPackage rec { 
+  pname = "cm-dashboard"; 
+  version = "0.1.0"; 
+  src = fetchFromGitea { 
+    domain = "gitea.cmtec.se"; 
+    owner = "cm"; 
+    repo = "cm-dashboard"; 
+    rev = "YOUR_COMMIT_HASH"; 
+    hash = "YOUR_SOURCE_HASH"; 
+  }; 
+  cargoHash = ""; 
+  nativeBuildInputs = [ pkg-config ]; 
+  buildInputs = [ openssl ]; 
+  buildAndTestSubdir = "."; 
+  cargoBuildFlags = [ "--workspace" ]; 
+}' 2>&1 | grep "got:"
+```
+
+Then update `cargoHash` in the configuration.
+
+#### 6. Commit the Changes
+```bash
+git add hosts/common/cm-dashboard.nix
+git commit -m "Update cm-dashboard to latest version"
+git push
+```
+
+### Example Update Process
+```bash
+# 1. Get latest commit
+LATEST_COMMIT=$(curl -s "https://gitea.cmtec.se/api/v1/repos/cm/cm-dashboard/commits?sha=main&limit=1" | grep '"sha"' | head -1 | cut -d'"' -f4)
+
+# 2. Get source hash
+SOURCE_HASH=$(nix-build --no-out-link -E "with import <nixpkgs> {}; fetchFromGitea { domain = \"gitea.cmtec.se\"; owner = \"cm\"; repo = \"cm-dashboard\"; rev = \"$LATEST_COMMIT\"; hash = \"sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=\"; }" 2>&1 | grep "got:" | cut -d' ' -f12)
+
+# 3. Update configuration and commit
+echo "Latest commit: $LATEST_COMMIT"
+echo "Source hash: $SOURCE_HASH"
+```