Add official formatter to flake

Allows running `nix fmt`, which will format using the official style as
agreed upon in nixpkgs

.editorconfig

@@ -6,7 +6,8 @@ end_of_line = lf
 insert_final_newline = true
 trim_trailing_whitespace = true
 charset = utf-8
-indent_style = tab
+indent_style = space
+indent_size = 2
 
 # Ignore diffs/patches
 [*.{diff,patch}]

flake.nix

@@ -85,7 +85,11 @@
         {
           inherit username;
 
-          checks = builtins.mapAttrs (system: deployLib: deployLib.deployChecks self.deploy) inputs.deploy-rs.lib;
+          checks = builtins.mapAttrs (
+            system: deployLib: deployLib.deployChecks self.deploy
+          ) inputs.deploy-rs.lib;
+
+          formatter."x86_64-linux" = inputs.unstable.legacyPackages."x86_64-linux".nixfmt-rfc-style;
 
           deploy.nodes = self.lib.deploy.mkDeployNodes self.nixosConfigurations {
             nachtigall = {