feat: Change parsers and add custom critic model (#838)

Author: shahules786

docs/howtos/customisations/index.md

@@ -4,6 +4,7 @@ How to Customize Ragas for Your Needs
 
 :::{toctree}
 ./bring-your-own-llm-or-embs
+ragas_custom_model.ipynb
 azure-openai.ipynb
 aws-bedrock.ipynb
 gcp-vertexai.ipynb