Update README

README.md

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+---
+license: other
+tags:
+- gwas
+- polygenic-risk-score
+- psychiatric-genetics
+- pgc
+---
+
+# Substance Use Disorders GWAS Summary Statistics (PGC)
+
+Mirror of Psychiatric Genomics Consortium (PGC) summary statistics for
+**Substance Use Disorders** (SUD2023), redistributed in a single Apache Parquet file
+for use with [OpenMed Genomics](https://huggingface.co/spaces/turmex2/openneuro-genomics).
+
+## Source
+
+- **Primary citation:** Hatoum et al., Nature Mental Health 2023
+- **Original distributor:** Psychiatric Genomics Consortium
+  (<https://pgc.unc.edu/for-researchers/download-results/>)
+
+This mirror exists only because the upstream OpenMed mirror became
+inaccessible. No modifications have been made to the underlying data;
+per-shard parquet files were concatenated into a single file for
+convenient streaming.
+
+## File
+
+`pgc-substance-use_SUD2023.parquet` -- one Apache Parquet file containing the full summary
+statistics table in the PGC's published schema (SNP, CHR, BP, A1, A2,
+FRQ, OR/BETA, SE, P, ...).
+
+## Usage
+
+```python
+import polars as pl
+df = pl.read_parquet(
+    "https://huggingface.co/datasets/turmex2/pgc-substance-use/resolve/main/pgc-substance-use_SUD2023.parquet"
+)
+```
+
+## License & terms of use
+
+PGC summary statistics are released for non-commercial research use only.
+Do not attempt to re-identify individuals.  Results derived from these
+data are **not** a clinical diagnosis.  See the original publication for
+the full data-use agreement.