[Doc] Add link to tool_choice tracking issue in tool_calling.md

docs/source/features/tool_calling.md

@@ -1,6 +1,6 @@
 # Tool Calling
 
-vLLM currently supports named function calling, as well as the `auto` and `none` options for the `tool_choice` field in the chat completion API. The `tool_choice` option `required` is **not yet supported** but on the roadmap.
+vLLM currently supports named function calling, as well as the `auto` and `none` options for the `tool_choice` field in the chat completion API. The `tool_choice` option `required` is **not yet supported** but [on the roadmap](https://github.com/vllm-project/vllm/issues/13002).
 
 ## Quickstart