README: add reviewer sample download instructions

README.md

@@ -14,9 +14,30 @@ ForceBody/
 │   └── <subject_id_raw>/trial_<idx>.npz
 ├── manifest.csv                        10,386 rows, one per trial
 ├── subjects.csv                        378 rows, one per subject_id_raw
+├── ForceBody_sample.tar.gz             100-trial reviewer sample (157 MB)
 └── README.md
 ```
 
+## Quick start for reviewers (small sample)
+
+The full release is roughly 19 GB. For a fast first look, download the 100-trial sample (157 MB), which carries the same per-trial schema as the full release.
+
+Direct download URL:
+
+```
+https://huggingface.co/datasets/ForceBody/ForceBody_ano/resolve/main/ForceBody_sample.tar.gz
+```
+
+Or with `wget` / `curl`:
+
+```bash
+wget https://huggingface.co/datasets/ForceBody/ForceBody_ano/resolve/main/ForceBody_sample.tar.gz
+tar -xzf ForceBody_sample.tar.gz
+ls ForceBody_sample/
+```
+
+The sample is stratified across all 10 source studies: 72 trials with Monte Carlo uncertainty and 28 skelfit-only trials, drawn with numpy seed 42. A `SAMPLE_README.md` inside the archive describes the selection. The schema documented in this README applies verbatim to every npz in the sample.
+
 `subject_id_raw` carries a study prefix where it is needed to disambiguate identical subject names across source datasets (`Moore2015__subject7` vs `Uhlrich2023__subject7`). Subjects unique within their source dataset (e.g. `P002_split0` from Carter2023) appear without the prefix.
 
 ## Composition