Update docs/versioned_docs/version-0.2.x/how_to/llm_token_usage_tracking.ipynb

Co-authored-by: ccurme <chester.curme@gmail.com>

docs/versioned_docs/version-0.2.x/how_to/llm_token_usage_tracking.ipynb

@@ -25,7 +25,7 @@
     "\n",
     "There are some API-specific callback context managers that allow you to track token usage across multiple calls. You'll need to check whether such an integration is available for your particular model.\n",
     "\n",
-    "If such an integration is not available for your model, you can create a custom callback manager by adapting the implementation of the OpenAI callback manager (find it in the code base and adapt for your own LLMs.)\n",
+    "If such an integration is not available for your model, you can create a custom callback manager by adapting the implementation of the [OpenAI callback manager](https://api.python.langchain.com/en/latest/_modules/langchain_community/callbacks/openai_info.html#OpenAICallbackHandler).\n",
     "\n",
     "### OpenAI\n",
     "\n",