HIP-RA-X README references

Author: softwareengineerprogrammer

src/hip_ra_x/README.md

@@ -1,3 +1,9 @@
-# HIP-RA-X
 
+# HIP-RA: Heat In Place - Resource Assessment
+
+See:
+1. [Heat in Place calculation: Muffler, P., and Raffaele Cataldi. "Methods for regional assessment of geothermal resources." Geothermics 7.2-4 (1978): 53-89.](https://github.com/NREL/GEOPHIRES-X/blob/95e21226faee12128b9ad5d5b12bbd662d02949b/References/Muffler-Cataldi_1978_%20HIP-RA.pdf)
+1. [Garg, S.K. and J. Combs. 2011.  A Reexamination of the USGS Volumetric "Heat in Place" Method. Stanford University, 36th Workshop on Geothermal Reservoir Engineering; SGP-TR-191, 5 pp.](https://github.com/NREL/GEOPHIRES-X/blob/95e21226faee12128b9ad5d5b12bbd662d02949b/References/Garg-Combs_2011_HIP-RA-Reexamination.pdf)
+
+## HIP-RA-X
 HIP-RA-X is the successor version to HIP-RA.