Added a usage example for SDL_GetWMInfo()

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401000

include/SDL_syswm.h

@@ -188,6 +188,11 @@ typedef struct SDL_SysWMinfo {
  * It fills the structure pointed to by 'info' with custom information and
  * returns 1 if the function is implemented.  If it's not implemented, or
  * the version member of the 'info' structure is invalid, it returns 0. 
+ *
+ * You typically use this function like this:
+ * SDL_SysWMInfo info;
+ * SDL_VERSION(&info.version);
+ * if ( SDL_GetWMInfo(&info) ) { ... }
  */
 extern DECLSPEC int SDLCALL SDL_GetWMInfo(SDL_SysWMinfo *info);