feat: Added docs via MkDocs

docs/defaultEvents/onInit.md

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+# `event` onInit
+This event is triggered when server successfully starts up.
+
+## Parameters
+No parameters.
+
+## Usage
+```python
+import g2o
+        
+@g2o.event('onInit')
+def onInitEventHandler(**kwargs):
+    print('Called onInit event')
+```