docs: Add use citation from ATLAS UEH MS displaced jet paper

[matthewfeickert]

Description

Add use citation from ATLAS paper Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in pp collisions at \sqrt{s}=13 TeV (ANA-EXOT-2019-24).

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* Add use citation from 'Search for events with a pair of displaced vertices
from long-lived neutral particles decaying into hadronic jets in the ATLAS
muon spectrometer in pp collisions at \sqrt{s}=13 TeV'
   - ATLAS paper: ANA-EXOT-2019-24
   - c.f. https://inspirehep.net/literature/2040545

[matthewfeickert]

Relevant RTD build: https://pyhf--1800.org.readthedocs.build/en/1800/citations.html#use-citations

[codecov]

Codecov Report

Merging #1800 (1582676) into master (8dedfeb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1800   +/-   ##
=======================================
  Coverage   98.12%   98.12%           
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  Files          64       64           
  Lines        4270     4270           
  Branches      683      683           
=======================================
  Hits         4190     4190           
  Misses         46       46           
  Partials       34       34           

Flag	Coverage Δ
contrib	26.25% <ø> (ø)
doctest	60.58% <ø> (ø)
unittests	96.18% <ø> (ø)

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