Upload external_waveplate pilot: data/README.md

data/README.md

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+# Data Shards
+
+Placeholder directory for full-resolution Parquet shards.
+
+Expected patterns:
+
+```text
+train-*.parquet                 # healthy_bone_cell
+validation-*.parquet            # healthy_bone_cell
+test-*.parquet                  # healthy_bone_cell
+external_waveplate-*.parquet    # generated pilot: 18 rows, 633 nm waveplate
+external_spectral_610-*.parquet
+external_spectral_650-*.parquet
+external_spectral_690-*.parquet
+```
+
+TODO: Replace this placeholder with generated Parquet shards.