Added nix flake and shell files for nixos users who want to work on development. You can use flake method => 'nix develop' or non flake method =>`nix-shell'

The shell.nix file is used for both flake and non-flake invocations. The lock file is also set at a version where the project works.
Note the none-flake method will follow the version of the system and isn't guaranteed to work on older installations if they haven't been updated in a while.
Added Documentation for using Nix package manager for development ./Documentation/LinuxDevelopmentSetupUsingNix.md

Signed-off-by: Ayman Jundi <ajundi@gmail.com>

Documentation/LinuxDevelopmentSetupUsingNix.md

@@ -0,0 +1,64 @@
+# Development Environment Setup using Nix or Nix Flakes on Linux x86_64
+[Nix flakes](https://nixos.wiki/wiki/Flakes) can be used to provide version controlled reproducible and cross-platform development environments. The key files are:
+- `flake.nix`: Defines the flake inputs and outputs, including development shells.
+- `shell.nix`: This file defines the dependencies and additionally adds support for the Impure `nix-shell` method. This is used by the flake to create the dev environment.
+- `flake.lock`: Locks the versions of inputs for reproducibility.
+---
+## Prerequisites
+- [Nix](https://nixos.org/download.html) the package manager or NixOs installed on Linux (x86_64-linux)
+- Optional: flakes support enabled. 
+---
+## Using the Development Shell
+You have two primary ways to enter the development shell with Nix:
+### 1. Using `nix develop` (flake-native command)
+This is the recommended way if you have Nix with flakes support. Flake guarantee the versions of the dependencies and can be controlled through `flake.nix` and `flake.lock`.
+```
+nix develop
+```
+This will open a shell with all dependencies and environment configured as per the `flake.nix` for (`x86_64-linux`) systems only at this time.
+
+---
+### 2. Using `nix-shell` (that's why shell.nix is a separate file)
+If you want to use traditional `nix-shell` tooling which uses the nixpkgs version of your system:
+```
+nix-shell
+```
+This will drop you into the shell environment defined in `shell.nix`. Note that this is not flake-native method and does not use the locked nixpkgs in `flake.lock` so exact versions of the dependancies is not guaranteed.
+
+---
+## What’s inside the dev shell?
+- The environment variables and packages configured in `shell.nix` will be available.
+- The package set (`pkgs`) used aligns with the versions locked in `flake.lock` to ensure reproducibility.
+
+---
+## Example Workflow using flakes
+```
+# Navigate to the project root folder which contains the flake.nix, flake.lock and shell.nix files.
+cd /home/user/dev/Libation
+# Enter the flake development shell (Linux x86_64)
+nix develop
+# run VSCode or VSCodium from the current shell environment
+code .
+# Run or Debug using VSCode and VSCodium using the linux Launch configuration.
+```
+![Debug using VSCode and VSCodium](./images/StartingDebuggingInVSCode.png)
+
+You can also Build and run your application inside the shell.
+``` 
+dotnet build ./Source/LibationAvalonia/LibationAvalonia.csproj -p:TargetFrameworks=net9.0 -p:TargetFramework=net9.0 -p:RuntimeIdentifier=linux-x64
+```
+
+---
+
+## Notes
+- Leaving the current shell environemnt will drop all added dependancies and you will not be able to run or debug the program unless your system has those dependancies defined globally.
+- To exit the shell environment voluntarily use `exit` inside the shell.
+- Ensure you have no conflicting `nix.conf` or `global.json` that might affect SDK versions or runtime identifiers.
+- Keep your `flake.lock` file committed to ensure builds are reproducible for all collaborators.
+
+---
+## References
+
+- [Nix Flakes - NixOS Wiki](https://nixos.wiki/wiki/Flakes)
+- [Nix.dev - Introduction to Nix flakes](https://nix.dev/manual/nix/2.28/command-ref/new-cli/nix3-flake-init)
+- [Nix-shell Manual](https://nixos.org/manual/nix/stable/command-ref/nix-shell.html)

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1749794982,
+        "narHash": "sha256-Kh9K4taXbVuaLC0IL+9HcfvxsSUx8dPB5s5weJcc9pc=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "ee930f9755f58096ac6e8ca94a1887e0534e2d81",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,16 @@
+{
+  description =
+    "Generic flake to run shell.nix with a locked nixos pkgs version. If you have
+    flakes enabled just run 'nix develop' in the same folder as flake.nix";
+  inputs = {
+    #// use your preferred nixpkgs version
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable"; 
+  };
+
+  outputs = { nixpkgs, ... }:
+    let
+      pkgs = nixpkgs.legacyPackages.x86_64-linux;
+    in {
+      devShells.x86_64-linux.default = import ./shell.nix {inherit pkgs;};
+    };
+}

shell.nix

@@ -0,0 +1,19 @@
+{pkgs ? import <nixpkgs> {}}: let
+  libPath = with pkgs;
+    lib.makeLibraryPath [
+      # load external libraries that you need in your dotnet project here
+      xorg.libX11
+      xorg.libICE
+      xorg.libSM
+      libGL
+      fontconfig
+    ];
+in
+  pkgs.mkShell {
+    buildInputs = with pkgs; [
+      dotnet-sdk_9
+    ];
+    
+    DOTNET_ROOT = "${pkgs.dotnet-sdk_9}/share/dotnet";
+    LD_LIBRARY_PATH =libPath;
+  }