win32: update compile txt to include dxmath and remove ddraw hint

win32/docs/how2compile.txt

@@ -6,20 +6,21 @@ NOTE: Unicode support requires a special zlib build - see the end of the zlib en
   your own project file for earlier MSVC versions. VS2017 will automatically ask to install
   the correct Windows SDK Version (7.1A)
 
-- A recent DirectX SDK. The official binary is compiled against the August 2009 SDK.
-  Note that as of the June 2010 release of the DirectX SDK, DirectDraw has been removed
-  (DirectDraw is disabled by default, DIRECTDRAW_SUPPORT enables it)
+- A recent DirectX SDK..
   https://www.microsoft.com/en-us/download/details.aspx?id=23549
 
+- DirecXMath. The source files should reside in win32/DirectXMath, or you can download them
+  automatically with "git submodule update --init".
+
 - zlib (optional, ZLIB define, enabled by default) - the default solution includes a zlib
   project that builds appropriately (force includes _tfwopen.h for unicode support in s9x).
-  The zlib directory should reside at win32/zlib/src, or you can download it automatically
-  with git submodule init && git submodule update.
+  The zlib source files should reside in win32/zlib/src, or you can download them automatically
+  with "git submodule update --init".
 
 - libpng (optional, HAVE_LIBPNG define, enabled by default) - the default solution includes
   a libpng project that builds appropriately.
-  The libpng directory should reside at win32/libpng/src, or you can download it automatically
-  with git submodule init && git submodule update.
+  The libpng source files should reside in win32/libpng/src, or you can download them automatically
+  with "git submodule update --init".
 
 - To compile Snes9x:
     Start up VS2017.