docs: Add published HEPData likelihoods to Use and Citations page (#781)

* Add BibTeX file for HEPData publication entries with HistFactory likelihoods
* Add list of HEPData published likelihoods to Use and Citations page

Author: matthewfeickert

docs/bib/HEPData_likelihoods.bib

@@ -0,0 +1,26 @@
+@misc{ins1771533,
+    title = "{Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in $\sqrt{s}$ = 13 TeV $pp$ collisions with the ATLAS detector}",
+    doi = "10.17182/hepdata.91127",
+    url = "https://doi.org/10.17182/hepdata.91127",
+    year = "2019",
+    type = "Data Collection",
+    collaboration = "ATLAS",
+}
+
+@misc{ins1765529,
+    title = "{Search for direct stau production in events with two hadronic $\tau$-leptons in $\sqrt{s} = 13$ TeV $pp$ collisions with the ATLAS detector}",
+    doi = "10.17182/hepdata.92006",
+    url = "https://doi.org/10.17182/hepdata.92006",
+    year = "2019",
+    type = "Data Collection",
+    collaboration = "ATLAS",
+}
+
+@misc{ins1748602,
+    title = "{Search for bottom-squark pair production with the ATLAS detector in final states containing Higgs bosons, $b$-jets and missing transverse momentum}",
+    doi = "10.17182/hepdata.89408",
+    url = "https://doi.org/10.17182/hepdata.89408",
+    year = "2019",
+    type = "Data Collection",
+    collaboration = "ATLAS",
+}

docs/citations.rst

@@ -1,14 +1,30 @@
 Use and Citations
 =================
 
+Citation
+--------
+
 The preferred BibTeX entry for citation of ``pyhf`` is
 
 .. literalinclude:: bib/preferred.bib
    :language: bibtex
 
+Use in Publications
+-------------------
+
 Updating list of citations and use cases of :code:`pyhf`:
 
 .. bibliography:: bib/use_citations.bib
    :list: bullet
    :all:
    :style: plain
+
+Published Likelihoods
+---------------------
+
+Updating list of HEPData entries for publications using ``HistFactory`` JSON likelihoods:
+
+.. bibliography:: bib/HEPData_likelihoods.bib
+   :list: bullet
+   :all:
+   :style: plain