docs: add section on Nix flake

docs/Developer Guide/Developer Guide/Building and deployment/Nix flake.md

@@ -0,0 +1,76 @@
+# Nix flake
+Since TriliumNext 0.94.1, the desktop and server applications can be built using [Nix](https://nixos.org/).
+
+## System requirements
+
+Installation of Nix on Mac or Linux ([download page](https://nixos.org/download/)). About 3-4 gigabytes of additional storage space, for build artifacts.
+
+## Run directly
+
+Using [nix run](https://nix.dev/manual/nix/stable/command-ref/new-cli/nix3-run.html), the desktop app can be started as: `nix run github:TriliumNext/Notes/v0.95.0`
+
+Running the server requires explicitly specifying the desired package: `nix run github:TriliumNext/Notes/v0.95.0#server`
+
+Instead of a version (`v0.95.0` above), you can also specify a commit hash (or a branch name). This makes it easy to test development builds.
+
+## Install on NixOS
+
+Add to your `flake.nix`:
+
+```
+{
+  inputs = {
+    nixpkgs.url = # ...;
+    trilium-notes = {
+      url = "github:TriliumNext/Notes/v0.95.0";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs =
+    {
+      self,
+      # ...
+      trilium-notes,
+      ...
+    }:
+    {
+      nixosConfigurations = {
+        "nixos" = nixpkgs.lib.nixosSystem {
+          system = "x86_64-linux";
+          modules = [
+            ./configuration.nix
+          ];
+          specialArgs = {
+            inherit
+              trilium-notes
+              ;
+          };
+        };
+      };
+    };
+}
+
+```
+
+Add to your `configuration.nix`:
+
+```
+{
+  # ...
+  trilium-notes,
+  ...
+}:
+
+{
+  # ...
+
+  services.trilium-server.package = trilium-notes.packages.x86_64-linux.server;
+
+  environment.systemPackages = [
+    trilium-notes.packages.x86_64-linux.desktop
+  ];
+}
+```
+
+The flake aims to be compatible with the latest NixOS stable and unstable.