add fallbacks to reliable completions()

docs/my-website/docs/completion/reliable_completions.md

@@ -1,6 +1,10 @@
 # Reliability for Completions()
 
-LiteLLM supports `completion_with_retries`. 
+LiteLLM supports the following functions for reliability:
+* `completion_with_retries`: use tenacity retries
+* `completion()` with fallback models: set `fallback_models=['gpt-3.5-turbo', 'command-nightly', 'llama2`]. If primary model fails try fallback models
+
+## Completion with Retries
 
 You can use this as a drop-in replacement for the `completion()` function to use tenacity retries - by default we retry the call 3 times. 
 
@@ -24,3 +28,50 @@ def test_completion_custom_provider_model_name():
     except Exception as e:
         printf"Error occurred: {e}")
 ```
+
+## Completion with Fallbacks
+LLM APIs can be unstable, completion() with fallbacks ensures you'll always get a response from your calls
+
+### Usage 
+To use fallback models with `completion()`, specify a list of models in the `fallbacks` parameter. 
+
+The `fallbacks` list should include the primary model you want to use, followed by additional models that can be used as backups in case the primary model fails to provide a response.
+
+```python
+response = completion(model="bad-model", fallbacks=["gpt-3.5-turbo" "command-nightly"], messages=messages)
+```
+
+## How does `completion_with_fallbacks()` work
+
+The `completion_with_fallbacks()` function attempts a completion call using the primary model specified as `model` in `completion()`. If the primary model fails or encounters an error, it automatically tries the fallback models in the specified order. This ensures a response even if the primary model is unavailable.
+
+### Output from calls
+```
+Completion with 'bad-model': got exception Unable to map your input to a model. Check your input - {'model': 'bad-model'
+
+
+
+completion call gpt-3.5-turbo
+{
+  "id": "chatcmpl-7qTmVRuO3m3gIBg4aTmAumV1TmQhB",
+  "object": "chat.completion",
+  "created": 1692741891,
+  "model": "gpt-3.5-turbo-0613",
+  "choices": [
+    {
+      "index": 0,
+      "message": {
+        "role": "assistant",
+        "content": "I apologize, but as an AI, I do not have the capability to provide real-time weather updates. However, you can easily check the current weather in San Francisco by using a search engine or checking a weather website or app."
+      },
+      "finish_reason": "stop"
+    }
+  ],
+  "usage": {
+    "prompt_tokens": 16,
+    "completion_tokens": 46,
+    "total_tokens": 62
+  }
+}
+
+```