SPIGOT-6746: Clarify PlayerPortalEvent documentation

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/event/player/PlayerPortalEvent.java

@@ -8,7 +8,7 @@ import org.jetbrains.annotations.Nullable;
 
 /**
  * Called when a player is about to teleport because it is in contact with a
- * portal.
+ * portal which will generate an exit portal.
  * <p>
  * For other entities see {@link org.bukkit.event.entity.EntityPortalEvent}
  */