feat: Add editorconfig

If prettier is called via treefmt-nix it does not source .editorconfig files
per default, hence the integration is enabled explicitly.

.editorconfig

@@ -0,0 +1,17 @@
+root = true
+
+[*]
+charset = utf-8
+trim_trailing_whitespace = true
+end_of_line = lf
+insert_final_newline = true
+indent_style = tabs
+
+[*.nix]
+indent_size = 2
+indent_style = space
+
+[*.md]
+indent_size = 2
+trim_trailing_whitespace = false
+

treefmt.nix

@@ -3,7 +3,10 @@ _: {
   projectRootFile = "flake.nix";
 
   # Files not to format.
-  settings.global.excludes = [ "LICENSE" ];
+  settings.global.excludes = [
+    ".editorconfig"
+    "LICENSE"
+  ];
 
   # nix
   programs.nixfmt.enable = true; # As of 2024-07-30 this is nixfmt-rfc-style.
@@ -11,5 +14,10 @@ _: {
   programs.deadnix.enable = true;
 
   # markdown
-  programs.prettier.enable = true;
+  programs.prettier = {
+    enable = true;
+    settings = {
+      editorconfig = true;
+    };
+  };
 }