fix: improve error message for invalid model path

- Add helpful guidance when model path does not exist
- Suggest verifying path correctness and GGUF file accessibility
- Addresses issue #2145 (Improve error messages)

Author: lxcxjxhx

llama_cpp/llama.py

@@ -374,7 +374,10 @@ def __init__(
         self.spm_infill = spm_infill
 
         if not os.path.exists(model_path):
-            raise ValueError(f"Model path does not exist: {model_path}")
+            raise ValueError(
+                f"Model path does not exist: {model_path}. "
+                f"Please verify the path is correct and the GGUF model file is accessible."
+            )
 
         self._model = self._stack.enter_context(
             contextlib.closing(