Move Nix files into a nix directory

Move everything from `config` to the root level.

nix/modules/home-manager/flameshot.nix

@@ -0,0 +1,16 @@
+{ username, ... }:
+{
+  services.flameshot = {
+    enable = true;
+
+    settings = {
+      General = {
+        disabledTrayIcon = false;
+        saveAfterCopy = true;
+        savePath = "/home/${username}/Pictures/Screenshots";
+        showHelp = false;
+        uiColor = "#60a5fa";
+      };
+    };
+  };
+}