docs: Add onnx exporting links (#271)

Some useful links are added to the exporting guide.

Author: javiermtorres

docs/getting-started.md

@@ -25,9 +25,16 @@ For exporting models to ONNX:
 > Requires Python 3.13+
 
 ```bash
-pip install optimum[exporters]
+pip install optimum[onnxruntime] onnxruntime
 ```
 
+There are some resources that you can check about the ONNX runtime, what HF models it supports, and how to export a model in HF to this format:
+
+* https://onnxruntime.ai/huggingface
+* https://huggingface.co/docs/optimum-onnx/onnx/usage_guides/export_a_model
+* https://huggingface.co/docs/transformers/serialization#onnx
+
+
 ## Your First Encoderfile
 
 Let's build a sentiment analysis model as an example.