docs: Added docs about onPlayer** events

docs/defaultEvents/player/onPlayerSpellCast.md

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+# `event` onPlayerSpellCast
+!!! note
+    Right now transformation and summon spells are not supported, despite this event will be triggered for them. Cancelling this event willl prevent this action to be synced to other players.
+    
+This event is triggered when player is casting some spell.
+
+Original: [onPlayerSpellCast](https://gothicmultiplayerteam.gitlab.io/docs/0.3.0/script-reference/server-events/player/onPlayerSpellCast/)
+
+## Parameters
+* `dict` **kwargs**:
+    * `int` **playerid**: the id of the player who casts the spell.
+    * `str | null` **instance**: the item instance from Daedalus scripts.
+    
+## Usage
+```python
+import g2o
+        
+@g2o.event('onPlayerSpellCast')
+def onSpellCast(**kwargs):
+    print(kwargs['player'], 'casted a spell', kwargs['instance'])
+```