[Doc] Convert docs to use colon fences (#12471)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/source/contributing/model/index.md

@@ -4,7 +4,7 @@
 
 This section provides more information on how to integrate a [PyTorch](https://pytorch.org/) model into vLLM.
 
-```{toctree}
+:::{toctree}
 :caption: Contents
 :maxdepth: 1
 
@@ -12,16 +12,16 @@ basic
 registration
 tests
 multimodal
-```
+:::
 
-```{note}
+:::{note}
 The complexity of adding a new model depends heavily on the model's architecture.
 The process is considerably straightforward if the model shares a similar architecture with an existing model in vLLM.
 However, for models that include new operators (e.g., a new attention mechanism), the process can be a bit more complex.
-```
+:::
 
-```{tip}
+:::{tip}
 If you are encountering issues while integrating your model into vLLM, feel free to open a [GitHub issue](https://github.com/vllm-project/vllm/issues)
 or ask on our [developer slack](https://slack.vllm.ai).
 We will be happy to help you out!
-```
+:::