add editorconfig

Signed-off-by: WaitSpring <me@waitspring.com>

.editorconfig

@@ -0,0 +1,8 @@
+[*]
+charset = utf-8
+indent_style = tab
+indent_size = 4
+tab_width = 4
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true