Add .editorconfig

As a portable way to ensure *.scd files will always use tabs.

.editorconfig

@@ -0,0 +1,10 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{scd,go}]
+indent_style = tab
+indent_size = 4