Migrate doc files to Markdown. (#24376)

* Rename index.mdx to index.md

* With saved modifs

* Address review comment

* Treat all files

* .mdx -> .md

* Remove special char

* Update utils/tests_fetcher.py

Co-authored-by: Lysandre Debut <lysandre.debut@reseau.eseo.fr>

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Co-authored-by: Lysandre Debut <lysandre.debut@reseau.eseo.fr>

docs/source/en/model_doc/open-llama.md

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+<!--Copyright 2023 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.
+
+⚠️ Note that this file is in Markdown but contain specific syntax for our doc-builder (similar to MDX) that may not be
+rendered properly in your Markdown viewer.
+
+-->
+
+# Open-Llama
+
+## Overview
+
+The Open-Llama model was proposed in [Open-Llama project](https://github.com/s-JoL/Open-Llama) by community developer s-JoL.
+
+The model is mainly based on LLaMA with some modifications, incorporating memory-efficient attention from Xformers, stable embedding from Bloom, and shared input-output embedding from PaLM.
+And the model is pre-trained on both Chinese and English, which gives it better performance on Chinese language tasks.
+
+This model was contributed by [s-JoL](https://huggingface.co/s-JoL).
+The original code can be found [Open-Llama](https://github.com/s-JoL/Open-Llama).
+Checkpoint and usage can be found at [s-JoL/Open-Llama-V1](https://huggingface.co/s-JoL/Open-Llama-V1).
+
+
+## OpenLlamaConfig
+
+[[autodoc]] OpenLlamaConfig
+
+## OpenLlamaModel
+
+[[autodoc]] OpenLlamaModel
+    - forward
+
+## OpenLlamaForCausalLM
+
+[[autodoc]] OpenLlamaForCausalLM
+    - forward
+
+## OpenLlamaForSequenceClassification
+
+[[autodoc]] OpenLlamaForSequenceClassification
+    - forward