docs: add reference for Saltelli sampling

docs/source/refs.bib

@@ -52,6 +52,16 @@
   author = "Meng Yang Gu and Jesus Palomo and James O. Berger",
 }
 
+@article{Herman2017, 
+  title = "{SALib}: An open-source {Python} library for Sensitivity Analysis", journal = "The Journal of Open Source Software",
+  volume = "2", 
+  number = "9",
+  page = "",
+  doi = "10.21105/joss.00097", 
+  year = "2017",
+  author = "Jon Herman and Will Usher"
+}
+
 @article{Mergili2017,
   AUTHOR = {Mergili, M. and Fischer, J. T. and Krenn, J. and Pudasaini, S. P.},
   TITLE = {r.avaflow v1, an advanced open-source computational framework for the propagation and interaction of two-phase mass flows},
@@ -63,6 +73,28 @@
   DOI = {10.5194/gmd-10-553-2017}
 }
 
+@article{Saltelli2002,
+  title = "Making best use of model evaluations to compute sensitivity indices",
+  journal = "Computer Physics Communications",
+  volume = "145",
+  number = "2",
+  pages = "280--297",
+  year = "2002",
+  doi = "https://doi.org/10.1016/S0010-4655(02)00280-1",
+  author = "Andrea Saltelli"
+}
+
+@article{Saltelli2010,
+  title = "Variance based sensitivity analysis of model output. {Design} and estimator for the total sensitivity index",
+  journal = "Computer Physics Communications",
+  volume = "181",
+  number = "2",
+  pages = "259--270",
+  year = "2010",
+  doi = "https://doi.org/10.1016/j.cpc.2009.09.018",
+  author = "Andrea Saltelli and Paola Annoni and Ivano Azzini and Francesca Campolongo and Marco Ratto and Stefano Tarantola"
+}
+
 @article{Zhao2021a,
   title   = "Emulator-based global sensitivity analysis for flow-like landslide run-out models",
   journal = "Landslides",