patch: added text to notebook explaining flow and flow-scaling

Author: taddyb

test/nhf/conecuh_case/README.md

@@ -10,3 +10,9 @@ cd test/nhf/conecuh_case
 uv pip install -r requirements.txt
 uv run python -m nwm_routing -V5 -f test_case.yaml
 ```
+
+# Streamflow Attribution
+
+Streamflow estimates in the `channel_forcing/` folder were obtained from the following paper/dataset:
+
+Song, Y., Bindas, T., Shen, C., Ji, H., Knoben, W. J. M., Lonzarich, L., et al. (2025). High-resolution national-scale water modeling is enhanced by multiscale differentiable physics-informed machine learning. Water Resources Research, 61, e2024WR038928. https://doi.org/10.1029/2024WR038928