docs: update llms.txt files

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Author: github-actions[bot]

docs/llms-full.txt

@@ -28917,6 +28917,11 @@ pip install 'datamodel-code-generator[http]'
 
 When the `output` parameter is omitted (or set to `None`), `generate()` returns the generated code directly as a string:
 
+!!! note
+    `GenerateConfig` is only available in Pydantic v2 environments.
+    For Pydantic v1, use `from datamodel_code_generator.config import GenerateConfig`
+    and call `update_forward_refs()` before use.
+
 ```python
 from datamodel_code_generator import InputFileType, generate, GenerateConfig, DataModelType