updated.

modules/sdl2/README.TXT

@@ -0,0 +1,5 @@
+Upgrading SDL source:
+
+* include/config_*.h need to be copied/merged from current mx2 version - this is where SDL features are enabled.
+
+* include/begin_code.h should #define DECLSPEC to empty at top to be able to statically link without msvc generating .lib and .exp files due to dllimport/dllexport symbols. Seems to be no #define SDL_STATIC_BUILD here?