docs: Add use citation from extended SPANet paper

[matthewfeickert]

Description

Add use citation from Extended Symmetry Preserving Attention Networks for LHC Analysis by Michael James Fenton, @Alexanders101, Hideki Okawa, Yuji Li, Ko-Yang Hsiao, @schsu, @danielwhiteson, Pierre Baldi.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Add use citation from 'Extended Symmetry Preserving Attention Networks
  for LHC Analysis'.
   - c.f. https://inspirehep.net/literature/2693496

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (444ee42) 98.30% compared to head (616f301) 98.30%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2315   +/-   ##
=======================================
  Coverage   98.30%   98.30%           
=======================================
  Files          69       69           
  Lines        4535     4535           
  Branches      802      802           
=======================================
  Hits         4458     4458           
  Misses         45       45           
  Partials       32       32           

Flag	Coverage Δ
contrib	97.88% <ø> (ø)
doctest	61.05% <ø> (ø)
unittests-3.10	96.31% <ø> (ø)
unittests-3.11	96.31% <ø> (ø)
unittests-3.8	96.33% <ø> (ø)
unittests-3.9	96.36% <ø> (ø)

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[matthewfeickert]

Relevant RTD build: https://pyhf--2315.org.readthedocs.build/en/2315/citations.html#use-citations