Add note about #130 to materials docs

doc/main.bib

@@ -1711,3 +1711,12 @@ @article{popp_2017_SSPlanduse
   volume = {42},
   year = {2017}
 }
+
+@article{unlu_2024_materials,
+  author = {Gamze Ünlü and Florian Maczek and Jihoon Min and Stefan Frank and Fridolin Glatter and Paul Natsuo Kishimoto and Jan Streeck and Nina Eisenmenger and Volker Krey and Dominik Wiedenhofer},
+  doi = {https://doi.org/10.5194/egusphere-2023-3035},
+  journal = {EGUsphere [preprint]},
+  title = {MESSAGEix-Materials v1.0.0: Representation of Material Flows and Stocks in an Integrated Assessment Model},
+  url = {https://egusphere.copernicus.org/preprints/2024/egusphere-2023-3035/},
+  year = {2024}
+}

doc/material/index.rst

@@ -18,6 +18,16 @@ Code reference
 .. automodule:: message_ix_models.data.material
   :members:
 
+.. note::
+   See also :pull:`130`/the archived branch `materials-migrate <https://github.com/iiasa/message-ix-models/tree/migrate-materials>`_ for a distinct version of :mod:`.material`.
+   That earlier PR was superseded by :pull:`188`, but contains the 1.0.0 version of MESSAGEix-Materials, which was used for the first submission of :cite:`unlu_2024_materials`. The model structure is almost identical to the default model that was added by :pull:`188`.
+   Compared to :pull:`188` this version differs particularly in the following areas:
+
+   - Older base year calibration of "other industries" using outdated IEA EWEB data
+   - Material demands computed in R through ``rpy2``, instead of Python implementation
+   - Less accurate regional allocation/aggregation of base year demands for cement and steel
+   - No use of :mod:`.tools.costs`
+
 Data preparation
 ----------------