fix(greylag): switch to wayland-native emacs

As niri doesn't have xwayland, emacs must use a build that can run on
native wayland. In future, this should probably be automatically chosen
when you have xwayland disabled (or wayland enabled) but currently it is
easy enough to do a per-user change

Change-Id: I822309668cd5144225dcf82491d98fd1317d4667
diff --git a/flake.nix b/flake.nix
index dc58a3b..5df0a55 100644
--- a/flake.nix
+++ b/flake.nix
@@ -69,6 +69,8 @@
     sops-nix.url = "github:Mic92/sops-nix";
 
     templates.url = "git+https://git.clicks.codes/Templates";
+
+    emacs-overlay.url = "github:nix-community/emacs-overlay";
   };
 
   outputs =
@@ -78,6 +80,7 @@
       src = ./.;
 
       overlays = [
+        inputs.emacs-overlay.overlays.default
         inputs.niri-flake.overlays.niri
       ];