[Docs] Add language identifiers to fenced code blocks (#28955)

Add language identifiers to code blocks

docs/source/en/model_doc/fastspeech2_conformer.md

@@ -41,7 +41,7 @@ You can run FastSpeech2Conformer locally with the 🤗 Transformers library.
 
 1. First install the 🤗 [Transformers library](https://github.com/huggingface/transformers), g2p-en:
 
-```
+```bash
 pip install --upgrade pip
 pip install --upgrade transformers g2p-en
 ```

docs/source/en/model_doc/layoutlmv2.md

@@ -50,7 +50,7 @@ this https URL.*
 
 LayoutLMv2 depends on `detectron2`, `torchvision` and `tesseract`. Run the
 following to install them:
-```
+```bash
 python -m pip install 'git+https://github.com/facebookresearch/detectron2.git'
 python -m pip install torchvision tesseract
 ```

docs/source/en/model_doc/lilt.md

@@ -39,7 +39,7 @@ The original code can be found [here](https://github.com/jpwang/lilt).
 - To combine the Language-Independent Layout Transformer with a new RoBERTa checkpoint from the [hub](https://huggingface.co/models?search=roberta), refer to [this guide](https://github.com/jpWang/LiLT#or-generate-your-own-checkpoint-optional).
 The script will result in `config.json` and `pytorch_model.bin` files being stored locally. After doing this, one can do the following (assuming you're logged in with your HuggingFace account):
 
-```
+```python
 from transformers import LiltModel
 
 model = LiltModel.from_pretrained("path_to_your_files")

docs/source/en/model_doc/musicgen.md

@@ -136,7 +136,7 @@ The same [`MusicgenProcessor`] can be used to pre-process an audio prompt that i
 following example, we load an audio file using the 🤗 Datasets library, which can be pip installed through the command
 below:
 
-```
+```bash
 pip install --upgrade pip
 pip install datasets[audio]
 ```

docs/source/en/model_doc/pop2piano.md

@@ -54,7 +54,7 @@ The original code can be found [here](https://github.com/sweetcocoa/pop2piano).
 ## Usage tips
 
 * To use Pop2Piano, you will need to install the 🤗 Transformers library, as well as the following third party modules:  
-```
+```bash
 pip install pretty-midi==0.2.9 essentia==2.1b6.dev1034 librosa scipy
 ```
 Please note that you may need to restart your runtime after installation.