[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

docs/source/troubleshooting.md

+<!---
+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 the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+# Troubleshooting
+
+This document is to help find solutions for common problems.
+
+## Firewalled environments
+
+Some cloud and intranet setups have their GPU instances firewalled to the outside world, so if your script is trying to download model weights or datasets it will first hang and then timeout with an error message like:
+
+```
+ValueError: Connection error, and we cannot find the requested files in the cached path.
+Please try again or make sure your Internet connection is on.
+```
+
+One possible solution in this situation is to use the ["offline-mode"](https://huggingface.co/transformers/installation.html#offline-mode).

src/transformers/modeling_utils.py

@@ -949,6 +949,12 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin, GenerationMixin):
 
             Passing :obj:`use_auth_token=True` is required when you want to use a private model.
 
+        .. note::
+
+            Activate the special `"offline-mode"
+            <https://huggingface.co/transformers/installation.html#offline-mode>`__ to use this method in a firewalled
+            environment.
+
         Examples::
 
             >>> from transformers import BertConfig, BertModel