The datasets/ directory is gitignored (large, re-downloadable), but later
agents need to know how to obtain the dataset when it is missing. Add a
tracked README that documents the download steps.
- datasets/README.md: documents the ShareGPT_V3_unfiltered_cleaned_split.json
source (HF anon8231489123/ShareGPT_Vicuna_unfiltered), the hf-mirror.com
download command for CN environments, the JSON validity check (94145
entries), and the container path consistency note.
- .gitignore: change "datasets/" to "datasets/*" so the "!datasets/README.md"
negation actually works (git cannot re-include a file under a fully-ignored
directory). The dataset .json stays ignored; only README.md is tracked.
