Theoretical basis summary update

Author: softwareengineerprogrammer

docs/Theoretical-Basis-for-GEOPHIRES.md

@@ -1,6 +1,10 @@
 # Theoretical Basis for GEOPHIRES
 
-This is adapted from [GEOPHIRES v2.0: updated geothermal techno-economic simulation tool](https://doi.org/10.1186/s40517-019-0119-6) (Koenraad F. Beckers & Kevin McCabe, 2019).
+> **Document Status: Historical (v2.0)**
+>
+> This document is adapted from the 2019 paper, "[GEOPHIRES v2.0: updated geothermal techno-economic simulation tool](https://doi.org/10.1186/s40517-019-0119-6)" by Koenraad Beckers & Kevin McCabe.
+>
+> The core theoretical explanations and equations herein have **not** been revised and reflect that version. While the lists of models have been minimally updated to link to newer documentation, the underlying theory for those additions is **not** described here. For the most accurate and up-to-date information, please consult the primary [project documentation](https://github.com/NREL/GEOPHIRES-X?tab=readme-ov-file#documentation).
 
 ## Built‑in models and correlations