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

Add language identifiers to code blocks

examples/research_projects/rag/README.md

@@ -45,7 +45,7 @@ We publish two `base` models which can serve as a starting point for finetuning
 The `base` models initialize the question encoder with [`facebook/dpr-question_encoder-single-nq-base`](https://huggingface.co/facebook/dpr-question_encoder-single-nq-base) and the generator with [`facebook/bart-large`](https://huggingface.co/facebook/bart-large).
 
 If you would like to initialize finetuning with a base model using different question encoder and generator architectures, you can build it with a consolidation script, e.g.:
-```
+```bash
 python examples/research_projects/rag/consolidate_rag_checkpoint.py \
     --model_type rag_sequence \
     --generator_name_or_path facebook/bart-large-cnn \