Point CONTRIBUTING.md at the shared PolicyEngine guide (#361)

Author: MaxGhenis

.github/CONTRIBUTING.md

@@ -1,7 +1,46 @@
-## Updating data
+# Contributing to policyengine-uk-data
 
-If your changes present a non-bugfix change to one or more datasets which are cloud-hosted (FRS and EFRS), then please change both the filename and URL (in both the class definition file and in `storage/upload_completed_datasets.py`). This enables us to store historical versions of datasets separately and reproducibly.
+See the [shared PolicyEngine contribution guide](https://github.com/PolicyEngine/.github/blob/main/CONTRIBUTING.md) for cross-repo conventions (towncrier changelog fragments, `uv run`, PR description format, anti-patterns). This file covers policyengine-uk-data specifics.
 
-## Updating the versioning
+## Commands
 
-Please add to `changelog.yaml` and then run `make changelog` before committing the results ONCE in this PR.
+```bash
+make install            # install deps (uv)
+make format             # format (required)
+make download           # download raw FRS + SPI inputs from HF (needs HUGGING_FACE_TOKEN)
+make data               # full dataset build (impute, calibrate, upload)
+make test               # test suite
+uv run pytest policyengine_uk_data/tests/path/to/test.py -v
+```
+
+Python 3.13+. Default branch: `main`. Raw FRS / SPI microdata live on HuggingFace; set `HUGGING_FACE_TOKEN` before running anything that touches the dataset build.
+
+## What lives here
+
+This repo builds the `.h5` files that feed `policyengine-uk`:
+
+- `datasets/frs.py` — raw FRS → PolicyEngine variable mapping
+- `datasets/imputations/` — QRF / other imputations layered on top (income, wealth, consumption, etc.)
+- `datasets/local_areas/` — constituency and local-authority calibration
+- `targets/` — calibration target sources (OBR, DWP, HMRC, ONS, SLC, etc.)
+- `utils/calibrate.py` — the reweighting optimiser
+- `storage/` — raw inputs, intermediate artefacts, published outputs
+
+## Data-protection rules — no exceptions
+
+The enhanced FRS dataset is licensed under strict UK Data Service terms. Violating them risks losing access, which would end PolicyEngine UK.
+
+- **Never upload data to any public location.** The HuggingFace repo `policyengine/policyengine-uk-data-private` is private and authenticated.
+- **Never modify `upload_completed_datasets.py` or `utils/data_upload.py`** to change upload destinations without explicit confirmation from the data controller (currently Nikhil Woodruff).
+- **Never print, log, or output individual-level records.** Aggregates (sums, means, counts, weighted totals) are fine; individual rows are not.
+- **If you see a private/public repo split, assume it is intentional** — ask why before changing it.
+
+## Updating datasets
+
+If your change is a non-bugfix update to a cloud-hosted dataset (FRS, enhanced FRS), bump both the filename and URL in the class definition and in `storage/upload_completed_datasets.py`. That lets us store historical dataset versions separately and reproducibly.
+
+## Repo-specific anti-patterns
+
+- **Don't** hardcode dataset years in variable transforms; use `dataset.time_period` and the uprating pipeline.
+- **Don't** commit large binary artefacts — use HuggingFace storage.
+- **Don't** skip `make test` when touching the imputation or calibration pipeline; full CI rebuilds the dataset and takes ~25 minutes.

changelog.d/docs-towncrier-contributing.changed.md

@@ -0,0 +1 @@
+Point CONTRIBUTING.md at the shared PolicyEngine contribution guide (https://github.com/PolicyEngine/.github) and trim the per-repo file to commands, repo-specific conventions, and anti-patterns. Removes the stale `changelog_entry.yaml` / `make changelog` instructions.