Updated script command npcskill documentation (#2691)

* Fixes #2681.
* NPCs must have basic stats applied to them for specific skills to work properly.
Thanks to @sader1992!

doc/script_commands.txt

@@ -7859,6 +7859,11 @@ and "NPC level" is the temporary level of the NPC (used in some skills).
 Neither value can be greater than the max level defined in config, and will
 not work properly if the NPC has a mob sprite.
 
+Before using skills, NPCs must have basic stats applied to them depending on the
+skill being used: UNPC_ATKMIN, UNPC_ATKMAX, UNPC_MATKMIN, UNPC_MATKMAX, UNPC_STR,
+UNPC_AGI, UNPC_VIT, UNPC_INT, UNPC_DEX, UNPC_LUK.
+See 'setunitdata' for more information on usage.
+
     // Casts Level 10 Heal on the attached player, calculated with
     // all stats 99 and base level 60.
     npcskill "AL_HEAL",10,99,60;