Fix dataset `amazon_us_reviews` metadata - 4/4/2022
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_4092). All of your documentation changes will be reflected on that endpoint.
Fixes #4048 by running `dataset-cli test` to reprocess data and regenerate metadata. Additionally I've updated the README to include up-to-date counts for the subsets.