[docs] Improve register_pipeline (#35300)

register_pipeline

docs/source/en/add_new_pipeline.md

@@ -184,7 +184,7 @@ class PairClassificationPipeline(Pipeline):
 ```
 
 The implementation is framework agnostic, and will work for PyTorch and TensorFlow models. If we have saved this in
-a file named `pair_classification.py`, we can then import it and register it like this:
+a file named `pair_classification.py`, we can then import it and register it like this. The [register_pipeline](https://github.com/huggingface/transformers/blob/9feae5fb0164e89d4998e5776897c16f7330d3df/src/transformers/pipelines/base.py#L1387) function registers the pipeline details (task type, pipeline class, supported backends) to a models `config.json` file.
 
 ```py
 from pair_classification import PairClassificationPipeline