Update USING_SWIFT.md

doc/USING_SWIFT.md

@@ -3,6 +3,7 @@
 If anyone has better solutions, tell me please or open a PR.
 
 ## Make Headers Public
+I'll simplify this very soon.
 There is an exception called `include non-modular headers` if compiling `fluwx` directly because `WeChatOpenSDK` uses static library.
 We have to make the headers in `WeChatOpenSDK` public in order to support swift: