[Doc] fix link for page that was renamed (#10455)

Signed-off-by: Russell Bryant <rbryant@redhat.com>

vllm/model_executor/model_loader/loader.py

@@ -105,7 +105,7 @@ def _initialize_model(vllm_config: VllmConfig, prefix: str = "") -> nn.Module:
     msg = ("vLLM model class should accept `vllm_config` and `prefix` as "
            "input arguments. Possibly you have an old-style model class"
            " registered from out of tree and it is used for new vLLM version. "
-           "Check https://docs.vllm.ai/en/latest/design/class_hierarchy.html "
+           "Check https://docs.vllm.ai/en/latest/design/arch_overview.html "
            "for the design and update the model class accordingly.")
     logger.warning(msg)
     logger.warning(