[troubleshooting] add 2 points of reference to the offline mode (#11236)

* add 2 points of reference to the offline mode

* link the new doc

* add error message

* Update src/transformers/modeling_utils.py

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* style

* rename

* Trigger CI

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

docs/source/index.rst

@@ -22,7 +22,7 @@ State-of-the-art NLP for everyone:
 - Hands-on practitioners
 - AI/ML/NLP teachers and educators
 
-.. 
+..
     Copyright 2020 The HuggingFace Team. All rights reserved.
 
     Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
@@ -394,6 +394,7 @@ TensorFlow and/or Flax.
 
     pretrained_models
     examples
+    troubleshooting
     custom_datasets
     notebooks
     sagemaker