docs: Add general use citation from 'Branches of a Tree' paper (#2312)

* Add general citation from 'Branches of a Tree: Taking Derivatives of
  Programs with Discrete and Branching Randomness in High Energy
  Physics'.
   - c.f. https://inspirehep.net/literature/2692444

docs/bib/general_citations.bib

@@ -1,3 +1,15 @@
+% 2023-08-31
+@article{Kagan:2023gxz,
+    author = "Kagan, Michael and Heinrich, Lukas",
+    title = "{Branches of a Tree: Taking Derivatives of Programs with Discrete and Branching Randomness in High Energy Physics}",
+    eprint = "2308.16680",
+    archivePrefix = "arXiv",
+    primaryClass = "stat.ML",
+    month = "8",
+    year = "2023",
+    journal = ""
+}
+
 % 2023-06-06
 @article{Eschle:2023ikn,
     author = "Eschle, J. and others",