Fix bad link to xP3 dataset

The previous link was https://huggingface.co/bigscience/xP3 which led to a 404. It is now corrected to https://huggingface.co/datasets/bigscience/xP3

README.md

@@ -707,7 +707,7 @@ model-index:
 - **Repository:** [bigscience-workshop/xmtf](https://github.com/bigscience-workshop/xmtf)
 - **Paper:** [Crosslingual Generalization through Multitask Finetuning](https://arxiv.org/abs/2211.01786)
 - **Point of Contact:** [Niklas Muennighoff](mailto:niklas@hf.co)
-- **Languages:** Refer to [mc4](https://huggingface.co/datasets/mc4) for pretraining & [xP3](https://huggingface.co/bigscience/xP3) for finetuning language proportions. It understands both pretraining & finetuning languages.
+- **Languages:** Refer to [mc4](https://huggingface.co/datasets/mc4) for pretraining & [xP3](https://huggingface.co/datasets/bigscience/xP3) for finetuning language proportions. It understands both pretraining & finetuning languages.
 - **BLOOMZ & mT0 Model Family:**
 
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