Add nix flake build instructions (#113)

Multiple commits are squashed into a single commit.

Add instructions on how to leverage Nix (with flakes) for reproducible
development environments.

Feedback is welcome.

src/en/general-development/setup/setting-up-a-development-environment.md

@@ -106,6 +106,51 @@ In Rider you can attach the resources directory to the solution so that you can
 
 ![](../../assets/images/setup-rider-attach-existing-folder.png)
 
+# Reproducible Development Environment with Nix/NixOS
+
+An easier way to set up your development environment for Linux users is to leverage Nix. Nix is a package manager and a functional domain specific language that allows one to declare anything from development environments to entire systems. In order to prevent the dreaded "it works on my machine" conundrum, we can declare a development environment in Nix that spawns an isolated reproducible shell.
+
+## Setting up Nix/NixOS with flakes
+
+You can [install Nix](https://nixos.org/download) either through installing the NixOS distribution itself or by using the script that is compatible with all Linux distributions that use systemd (Ubuntu, Fedora, Mint etc). For the sake of simplicity and convenience, it is recommended that you install Nix in a distribution that you are comfortable with instead of making the jump to a different operating system entirely. It is also possible to use Nix with MacOS through `nix-darwin` though this has not been tested as of yet and thus not covered in this article.
+
+Once Nix is installed, you should enable experimental features such as flakes. If you are on a non-NixOS distribution, you can just add the following to your `~/.config/nix/nix.conf`.
+
+* `experimental-features = nix-command flakes`
+
+If you're using NixOS, you only need to add these options to your `configuration.nix` file.
+
+* `nix.settings.experimental-features = [ "nix-command" "flakes" ];`
+
+For more information about how to enable Nix flakes, see [here](https://nixos.wiki/wiki/Flakes).
+
+## Using Nix flakes for a Robust Development Environment
+
+NB it is technically required that you already have Git installed but in the case with most Linux distributions it comes preinstalled. In the highly unlikely case that you do not:
+
+* Use your distribution's package manager
+
+* Declare it in your `configuration.nix` file if you're using NixOS. It's recommended that you check the [appropriate section in the NixOS manual](https://nixos.org/manual/nixos/stable/#sec-configuration-file) but in short you should add `pkgs.git` into the `environment.systemPackages` attribute.
+
+Using your terminal you can simply navigate to the root directory of your SS14 repo and run:
+
+* `nix develop`
+
+Nix will automatically handle all dependencies as declared by `shell.nix` and called by the `flake.nix` file. You will have a new ephemeral shell (known as a `devShell`) that has everything that you need installed to build SS14 from source.
+
+This remains the reason as to why flakes are highly recommended despite being considered an experimental feature. We can make sure that everyone has the same versions of dependencies by specifying the nixpkgs collection version in the input attribute of the flake and locking the versions in a `flake.lock` file. In this way, all contributors that use Nix/NixOS get to have the exact same development environment. No pun intended, but that is pretty robust!
+
+## (Optional) Run JetBrains Rider through Nix
+
+You can then use either use an editor or IDE of your choosing. However within the shell that you already spawned you can just specify that you require JetBrains Rider. Run this command in your devShell.
+
+* `NIXPKGS_ALLOW_UNFREE=1 nix shell nixpkgs#jetbrains.rider --impure`
+
+From your new shell you can start a "detached" JetBrains Rider process by running something like:
+
+* `nohup rider >/dev/null 2>&1 &`
+
+And voila! You have robustly set up your development environment in a way that doesn't result in pesky buildup of "state". You can practically work on SS14 from any Linux distribution (granted that they use systemd) without irreversibly changing your system.
 
 # Troubleshooting