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

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

docs/source/contributing/model/basic.md

@@ -10,9 +10,9 @@ First, clone the PyTorch model code from the source repository.
 For instance, vLLM's [OPT model](gh-file:vllm/model_executor/models/opt.py) was adapted from
 HuggingFace's [modeling_opt.py](https://github.com/huggingface/transformers/blob/main/src/transformers/models/opt/modeling_opt.py) file.
 
-```{warning}
+:::{warning}
 Make sure to review and adhere to the original code's copyright and licensing terms!
-```
+:::
 
 ## 2. Make your code compatible with vLLM
 
@@ -80,10 +80,10 @@ def forward(
     ...
 ```
 
-```{note}
+:::{note}
 Currently, vLLM supports the basic multi-head attention mechanism and its variant with rotary positional embeddings.
 If your model employs a different attention mechanism, you will need to implement a new attention layer in vLLM.
-```
+:::
 
 For reference, check out our [Llama implementation](gh-file:vllm/model_executor/models/llama.py). vLLM already supports a large number of models. It is recommended to find a model similar to yours and adapt it to your model's architecture. Check out <gh-dir:vllm/model_executor/models> for more examples.