Update theoretical basis summary to clarify relevance to current/future versions.

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).
+This document describes the foundational theoretical basis for GEOPHIRES, 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 F. Beckers & Kevin McCabe. The core theories described here remain valid and relevant to the current software.
+
+However, the text has not been comprehensively updated to include the theory for features added in GEOPHIRES v3 (GEOPHIRES-X) and later.
+While pointers to the documentation for newer models have been added, the detailed technical descriptions herein still pertain to v2.0.
+For a complete and current reference, please see the [README](https://github.com/NREL/GEOPHIRES-X?tab=readme-ov-file#documentation).
 
 ## Built‑in models and correlations