Added a python script to rename SDL2 headers to SDL3 headers

docs/README-migration.md

@@ -9,7 +9,10 @@ Many functions and symbols have been renamed. We have provided a handy Python sc
 rename_symbols.py --all-symbols source_code_path
 ```
 
-SDL headers should now be included as `#include <SDL3/SDL.h>`. Typically that's the only header you'll need in your application unless you are using OpenGL or Vulkan functionality.
+SDL headers should now be included as `#include <SDL3/SDL.h>`. Typically that's the only header you'll need in your application unless you are using OpenGL or Vulkan functionality. We have provided a handy Python script [rename_headers.py](https://github.com/libsdl-org/SDL/blob/main/build-scripts/rename_headers.py) to rename SDL2 headers to their SDL3 counterparts:
+```sh
+rename_headers.py source_code_path
+```
 
 The file with your main() function should also include <SDL3/SDL_main.h>, see below in the SDL_main.h section.