Add helpful references for geogebra file in readme

readme.md

@@ -127,6 +127,12 @@ For more information look at the GitHub from the [lichess-bot](https://github.co
 
 A Geogebra file `Mean_max.gbb` for exploring how to get the minimum and maximum of two gaussian distributions.
 
+These two papers have been quite helpful for this part:
+
+* *Exact Distribution of the Max/Min of Two Gaussian Random Variables* by *Saralees Nadarajah and Samuel Kotz*
+* *Speeding up Computation of the max/min of a set of Gaussians for Statistical Timing Analysis and Optimization* by *Kuruvilla et al.*
+
+
 ## Credits
 
 Lukas Kuess, Stefan Steiniger, Theo Haslinger, Lukas Wieser