docs: Add use citation from revisiting mono-tau tails at the LHC paper

[matthewfeickert]

Description

Add use citation from Revisiting mono-τ tails at the LHC by Florentin Jaffredo.

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* Add use citation from Revisiting mono-τ tails at the LHC by Florentin Jaffredo.
   - c.f. https://inspirehep.net/literature/1998227

[matthewfeickert]

Relevant RTD build: https://pyhf--1744.org.readthedocs.build/en/1744/citations.html#use-in-publications

[codecov]

Codecov Report

Merging #1744 (5c361d2) into master (ba8fb4c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1744   +/-   ##
=======================================
  Coverage   98.12%   98.12%           
=======================================
  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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