Add config for nix-shell (#1359)

* Add config for nix-shell

This adds a development environment for Nix users, which automatically installs all libraries needed for building and fixes some nix stuff.

* Add Mold

This adds the Mold-Linker to improve build times. I also added an alias,
so cargo is run through mold.

shell.nix

@@ -0,0 +1,63 @@
+# This is a helper file for people using NixOs as their Operating System
+# > If you don't know what this file does you can safely ignore it :D
+
+# If you are using nix as your package manager, you can run 'nix-shell'
+# in the root directory of the project and nix will open a bash shell
+# with all the packages needed to build and run Graphite installed.
+# A shell.nix file is used in the Nix ecosystem to define a development
+# environment with specific dependencies. When you enter a Nix shell using
+# this file, it ensures that all the specified tools and libraries are
+# available regardless of the host system's configuration. This provides
+# a reproducible development environment across different machines and developers.
+
+# If you don't need the shell, you can build Graphite using this command:
+# nix-shell --command "npm start"
+
+let
+  # Get oxalica's Rust overlay for better Rust integration
+  rust-overlay-source = builtins.fetchGit {
+    url = "https://github.com/oxalica/rust-overlay";
+  };
+
+  # Import it so we can use it in Nix
+  rust-overlay = import rust-overlay-source;
+
+  # Import system packages overlaid with the Rust overlay
+  pkgs = import <nixpkgs> {
+    overlays = [ rust-overlay ];
+  };
+
+  # Define the rustc we need
+  rustc-wasm = pkgs.rust-bin.stable.latest.default.override {
+    targets = [ "wasm32-unknown-unknown" ];
+    # wasm-pack needs this
+    extensions = [ "rust-src" ];
+  };
+in
+  # Make a shell with the dependencies we need
+  pkgs.mkShell {
+    packages = [
+      rustc-wasm
+      pkgs.nodejs
+      pkgs.cargo
+      pkgs.cargo-watch
+      pkgs.wasm-pack
+
+      pkgs.openssl
+      pkgs.glib
+      pkgs.gtk3
+      pkgs.libsoup
+      pkgs.webkitgtk
+
+      pkgs.pkg-config
+
+      # Use Mold as a Linke
+      pkgs.mold
+    ];
+
+    # Hacky way to run cago through Mold
+    shellHook = ''
+    alias cargo='mold --run cargo'
+    '';
+  }
+