docs: Added docs about onPlayer** events

docs/defaultEvents/player/onPlayerJoin.md

@@ -0,0 +1,17 @@
+# `event` onPlayerJoin
+This event is triggered when a player successfully joined the server.
+
+Original: [onPlayerJoin](https://gothicmultiplayerteam.gitlab.io/docs/0.3.0/script-reference/server-events/player/onPlayerJoin/)
+
+## Parameters
+* `dict` **kwargs**:
+    * `int` **playerid**: the id of the player who joined the server.
+    
+## Usage
+```python
+import g2o
+        
+@g2o.event('onPlayerJoin')
+def onJoin(**kwargs):
+    print(kwargs['playerid'], 'joined to the server.')
+```