update README

Author: svirpioj

README.md

@@ -124,3 +124,44 @@ matrix) and `scale=0.5` (recommended). For SWA, you should use
   * `MarianPreTrainedModel` -> `SwagMarianPreTrainedModel`
   * `MarianModel` -> `SwagMarianModel`
   * `MarianMTModel` -> `SwagMarianMTModel`
+
+### Registering classes for transformers Auto methods
+
+As the SWAG variants are not part of the Hugging Face libraries, you
+need to register them in order for `AutoModelForXXX` methods to
+work. For example, for `SwagBertForSequenceClassification` you need to
+have:
+
+```python
+transformers.AutoConfig.register("swag_bert", SwagBertConfig)
+transformers.AutoModelForSequenceClassification.register(SwagBertConfig, SwagBertForSequenceClassification)
+```
+
+Now you can load a saved model with:
+
+```python
+transformers.AutoModelForSequenceClassification.from_pretrained(path)
+```
+
+### Wrapping custom models
+
+It is easy to wrap any model class based on the `transformers`
+library. For example, having `MyModel` with `MyModelConfig`, you can
+define the SWAG variants as follows:
+
+```python
+from swag_transformers.base import SwagConfig, SwagModel
+
+MODEL_TYPE = 'swag_mymodel'
+
+class SwagMyModelConfig(SwagConfig):
+
+    model_type = MODEL_TYPE
+    internal_config_class = MyModelConfig
+
+class SwagMyModel(SwagModel):
+
+    base_model_prefix = MODEL_TYPE
+    config_class = SwagMyModelConfig
+    internal_model_class = MyModel
+```