Improve "Exists" description

Based on this: https://www.gibberlings3.net/forums/topic/38976-does-exists-trigger-works-as-described/

scripting/triggers/bgeetriggers.htm

@@ -91,7 +91,7 @@
 
 <div class="triggerHeader"><a name="0x400D">0x400D Exists(O:Object*)</a></div>
 <div class="indent1">
-  Returns true only if the specified object exists in the current area (note that dead creatures can still be counted as existing).
+  Returns true only if the specified object exists in the current area (note that dead creatures can still be counted as existing). For the global objects (creatures that get stored in the GAM file, like NPCs that were joined in the past) it always returns true.
 </div>
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