refactor: move flake-parts modules to nix/modules/flake

nix/files/cheatsheet.nix

@@ -0,0 +1,17 @@
+{ lib, config, ... }:
+let
+  inherit (lib) concatStringsSep singleton;
+in
+{
+  text.cheatsheet = concatStringsSep "\n" [
+    "`__curPos.file` will give the full evaluated path of the nix file it is called in. See [this issue](https://github.com/NixOS/nix/issues/5897#issuecomment-1012165198) for more information."
+  ];
+  perSystem =
+    { pkgs, ... }:
+    {
+      files.files = singleton {
+        path_ = "docs/cheatsheet.md";
+        drv = pkgs.writeText "cheatsheet.md" config.text.cheatsheet;
+      };
+    };
+}

nix/files/readme.nix

@@ -0,0 +1,25 @@
+{ config, ... }:
+{
+  text.readme = {
+    heading = "Pantheon";
+    description = # markdown
+      ''
+        This flake serves as a monorepo for my systems (using IaC), dotfiles, and scripts.
+      '';
+    parts."Structure" = # markdown
+      ''
+        The system configurations are defined in [`flake.manifest`](nix/manifest.nix).
+      '';
+  };
+
+  perSystem =
+    { pkgs, ... }:
+    {
+      files.files = [
+        {
+          path_ = "README.md";
+          drv = pkgs.writeText "README.md" config.text.readme;
+        }
+      ];
+    };
+}