Add contributing guideline and mypy config (#122)

cacheflow/model_executor/model_loader.py

@@ -1,4 +1,6 @@
 """Utilities for selecting and loading models."""
+from typing import Type
+
 import torch
 import torch.nn as nn
 from transformers import PretrainedConfig
@@ -17,7 +19,7 @@ _MODEL_REGISTRY = {
 }
 
 
-def _get_model_architecture(config: PretrainedConfig) -> nn.Module:
+def _get_model_architecture(config: PretrainedConfig) -> Type[nn.Module]:
     architectures = getattr(config, "architectures", [])
     for arch in architectures:
         if arch in _MODEL_REGISTRY: