docs: Add SModelS paper to citations list (#1055)

* Add SModelS paper on SModelS v1.2.4 pyhf interface and use of public likelihoods
   - c.f. https://inspirehep.net/literature/1814793

Author: matthewfeickert

docs/bib/use_citations.bib

@@ -1,3 +1,14 @@
+@article{Alguero:2020grj,
+    author = "Alguero, Gaël and Kraml, Sabine and Waltenberger, Wolfgang",
+    title = "{A SModelS interface for pyhf likelihoods}",
+    eprint = "2009.01809",
+    archivePrefix = "arXiv",
+    primaryClass = "hep-ph",
+    month = "Sep",
+    year = "2020",
+    journal = ""
+}
+
 @article{Abdallah:2020pec,
       author         = "Abdallah, Waleed and others",
       title          = "{Reinterpretation of LHC Results for New Physics: Status