nix: add flake with dev shell

.editorconfig

@@ -1,15 +1,17 @@
 root = true
 
 [*]
-end_of_line = lf
-insert_final_newline = true
 indent_style = space
 indent_size = 4
+tab_width = 4
+end_of_line = lf
 charset = utf-8
 trim_trailing_whitespace = true
-
-[*.yml]
-indent_size = 2
+insert_final_newline = true
 
 [*.md]
 trim_trailing_whitespace = false
+
+[*.{md,nix,yml,yaml}]
+indent_size = 2
+tab_width = 2