Add an EditorConfig file

See https://editorconfig.org/ for more information.

.editorconfig

+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_style = space
+indent_size = 2
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.lua]
+indent_style = tab
+indent_size = 4