Android: Added to APK expansion file hint documentation in header file.

include/SDL_hints.h

@@ -532,14 +532,28 @@ extern "C" {
 *
 */
 #define SDL_HINT_MAC_BACKGROUND_APP    "SDL_MAC_BACKGROUND_APP"
-    
+
 /**
  * \brief Android APK expansion main file version. Should be a string number like "1", "2" etc.
+ *
+ * Must be set together with SDL_HINT_ANDROID_APK_EXPANSION_PATCH_FILE_VERSION.
+ *
+ * If both hints were set then SDL_RWFromFile() will look into expansion files
+ * after a given relative path was not found in the internal storage and assets.
+ *
+ * By default this hint is not set and the APK expansion files are not searched.
  */
 #define SDL_HINT_ANDROID_APK_EXPANSION_MAIN_FILE_VERSION "SDL_ANDROID_APK_EXPANSION_MAIN_FILE_VERSION"
 
 /**
  * \brief Android APK expansion patch file version. Should be a string number like "1", "2" etc.
+ *
+ * Must be set together with SDL_HINT_ANDROID_APK_EXPANSION_MAIN_FILE_VERSION.
+ *
+ * If both hints were set then SDL_RWFromFile() will look into expansion files
+ * after a given relative path was not found in the internal storage and assets.
+ *
+ * By default this hint is not set and the APK expansion files are not searched.
  */
 #define SDL_HINT_ANDROID_APK_EXPANSION_PATCH_FILE_VERSION "SDL_ANDROID_APK_EXPANSION_PATCH_FILE_VERSION"