docs: add repository documentation with upstream attribution

README.md

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+---
+license: apache-2.0
+pretty_name: SciExp Fixtures
+tags:
+  - test-fixtures
+  - duckdb
+  - ducklake
+size_categories:
+  - n<1K
+---
+
+# sciexp/fixtures
+
+Test fixtures and example datasets for [sciexp](https://github.com/sciexp).
+
+## Quick start
+
+```sh
+git clone https://huggingface.co/datasets/sciexp/fixtures
+cd fixtures
+git lfs pull
+```
+
+## Datasets
+
+### Space dataset
+
+A relational dataset about space exploration demonstrating DuckLake workflows.
+Contains tables for astronauts, missions, spacecraft, and mission crew assignments.
+
+```sh
+duckdb -box < queries/space.sql
+```
+
+<details>
+<summary>Manual DuckDB session</summary>
+
+Attach directly from Hugging Face:
+
+```sql
+INSTALL ducklake;
+LOAD ducklake;
+ATTACH 'ducklake:hf://datasets/sciexp/fixtures/lakes/frozen/space.db' AS space;
+SHOW TABLES FROM space.main;
+```
+
+Or from a local clone:
+
+```sql
+ATTACH 'ducklake:lakes/frozen/space.db' AS space;
+```
+
+</details>
+
+## Attribution
+
+The space missions dataset originates from:
+
+- [marhar/frozen](https://github.com/marhar/frozen) - Frozen DuckLake Demo
+- [marhar/duckdb_tools](https://github.com/marhar/duckdb_tools) - DuckDB tools including frozen-ducklake workflow scripts
+
+## Repository layout
+
+<details>
+<summary>Directory structure</summary>
+
+```
+lakes/frozen/                DuckLake databases
+  space.db                   Metadata database
+  space/                     Parquet data files
+queries/                     SQL scripts
+```
+
+</details>
+
+## Contributing
+
+<details>
+<summary>Authentication and push workflow</summary>
+
+Push access requires Hugging Face authentication:
+
+```sh
+hf auth login --token "${HF_TOKEN}" --add-to-git-credential
+```
+
+Push changes:
+
+```sh
+git lfs push --all origin
+git push
+```
+
+</details>