[Model] Add base class for LoRA-supported models (#5018)

docs/source/models/lora.rst

@@ -4,6 +4,9 @@ Using LoRA adapters
 ===================
 
 This document shows you how to use `LoRA adapters <https://arxiv.org/abs/2106.09685>`_ with vLLM on top of a base model.
+
+LoRA adapters can be used with any vLLM model that implements :class:`~vllm.model_executor.models.interfaces.SupportsLoRA`.
+
 Adapters can be efficiently served on a per request basis with minimal overhead. First we download the adapter(s) and save
 them locally with