add custom callback to docs

docs/my-website/docs/observability/custom_callback.md

@@ -0,0 +1,48 @@
+# Custom Callback Functions for Completion()
+
+## Defining a Custom Callback Function
+Create a custom callback function that takes specific arguments:
+
+```python
+def custom_callback(
+    kwargs,                 # kwargs to completion
+    completion_response,    # response from completion
+    start_time, end_time    # start/end time
+):
+    # Your custom code here
+```
+
+## Using Your Custom Callback Function
+
+```python
+import litellm
+from litellm import completion
+
+# Assign the custom callback function
+litellm.success_callback = [custom_callback]
+
+response = completion(
+    model="gpt-3.5-turbo",
+    messages=[
+        {
+            "role": "user",
+            "content": "Hi 👋 - i'm openai"
+        }
+    ]
+)
+
+print(response)
+
+```
+
+
+
+
+
+
+
+
+
+
+
+

docs/my-website/sidebars.js

@@ -90,6 +90,7 @@ const sidebars = {
       items: [
         "observability/callbacks",
         "observability/integrations",
+        "observability/custom_callback",
         "observability/promptlayer_integration",
         "observability/langfuse_integration",
         "observability/traceloop_integration",