Added/modified documentation for function arguments.

windows/win.c

diff --git a/windows/win.c b/windows/win.c
index 60569e1..bfe006f 100644
--- a/windows/win.c
+++ b/windows/win.c
@@ -2187,9 +2187,9 @@
  *
  */
 LONG WINAPI SetWindowLongW( 
-    HWND hwnd, /* window to alter */
-    INT offset, /* offset, in bytes, of location to alter */
-    LONG newval  /* new value of location */
+    HWND hwnd,  /* [in] window to alter */
+    INT offset, /* [in] offset, in bytes, of location to alter */
+    LONG newval /* [in] new value of location */
 ) {
     return WIN_SetWindowLong( hwnd, offset, newval, WIN_PROC_32W );
 }