Convert model files from rst to mdx (#14865)

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

docs/source/model_doc/camembert.mdx

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+
+Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
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+http://www.apache.org/licenses/LICENSE-2.0
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+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.
+-->
+
+# CamemBERT
+
+## Overview
+
+The CamemBERT model was proposed in [CamemBERT: a Tasty French Language Model](https://arxiv.org/abs/1911.03894) by
+Louis Martin, Benjamin Muller, Pedro Javier Ortiz Suárez, Yoann Dupont, Laurent Romary, Éric Villemonte de la
+Clergerie, Djamé Seddah, and Benoît Sagot. It is based on Facebook's RoBERTa model released in 2019. It is a model
+trained on 138GB of French text.
+
+The abstract from the paper is the following:
+
+*Pretrained language models are now ubiquitous in Natural Language Processing. Despite their success, most available
+models have either been trained on English data or on the concatenation of data in multiple languages. This makes
+practical use of such models --in all languages except English-- very limited. Aiming to address this issue for French,
+we release CamemBERT, a French version of the Bi-directional Encoders for Transformers (BERT). We measure the
+performance of CamemBERT compared to multilingual models in multiple downstream tasks, namely part-of-speech tagging,
+dependency parsing, named-entity recognition, and natural language inference. CamemBERT improves the state of the art
+for most of the tasks considered. We release the pretrained model for CamemBERT hoping to foster research and
+downstream applications for French NLP.*
+
+Tips:
+
+- This implementation is the same as RoBERTa. Refer to the [documentation of RoBERTa](roberta) for usage examples
+  as well as the information relative to the inputs and outputs.
+
+This model was contributed by [camembert](https://huggingface.co/camembert). The original code can be found [here](https://camembert-model.fr/).
+
+## CamembertConfig
+
+[[autodoc]] CamembertConfig
+
+## CamembertTokenizer
+
+[[autodoc]] CamembertTokenizer
+    - build_inputs_with_special_tokens
+    - get_special_tokens_mask
+    - create_token_type_ids_from_sequences
+    - save_vocabulary
+
+## CamembertTokenizerFast
+
+[[autodoc]] CamembertTokenizerFast
+
+## CamembertModel
+
+[[autodoc]] CamembertModel
+
+## CamembertForCausalLM
+
+[[autodoc]] CamembertForCausalLM
+
+## CamembertForMaskedLM
+
+[[autodoc]] CamembertForMaskedLM
+
+## CamembertForSequenceClassification
+
+[[autodoc]] CamembertForSequenceClassification
+
+## CamembertForMultipleChoice
+
+[[autodoc]] CamembertForMultipleChoice
+
+## CamembertForTokenClassification
+
+[[autodoc]] CamembertForTokenClassification
+
+## CamembertForQuestionAnswering
+
+[[autodoc]] CamembertForQuestionAnswering
+
+## TFCamembertModel
+
+[[autodoc]] TFCamembertModel
+
+## TFCamembertForMaskedLM
+
+[[autodoc]] TFCamembertForMaskedLM
+
+## TFCamembertForSequenceClassification
+
+[[autodoc]] TFCamembertForSequenceClassification
+
+## TFCamembertForMultipleChoice
+
+[[autodoc]] TFCamembertForMultipleChoice
+
+## TFCamembertForTokenClassification
+
+[[autodoc]] TFCamembertForTokenClassification
+
+## TFCamembertForQuestionAnswering
+
+[[autodoc]] TFCamembertForQuestionAnswering