Clarify that you shouldn't make any assumptions about the an SDL_FingerID value.

Fixes https://github.com/libsdl-org/SDL/issues/11667

include/SDL3/SDL_touch.h

@@ -53,12 +53,7 @@ typedef Uint64 SDL_TouchID;
 /**
  * A unique ID for a single finger on a touch device.
  *
- * This ID is valid for the time the finger (stylus, etc) is touching, and is
- * never reused for the lifetime of the application.
- *
- * The same physical finger will have a different ID if it lifts off the touch
- * device and then starts a new touch, so this ID tracks the lifetime of a
- * single continuous touch.
+ * This ID is valid for the time the finger (stylus, etc) is touching and will be unique for all fingers currently in contact, so this ID tracks the lifetime of a single continuous touch. This value may represent an index, a pointer, or some other unique ID, depending on the platform.
  *
  * The value 0 is an invalid ID.
  *