docs: Add use citation from Belle II evidence for B+→K+νν¯ decays paper

[matthewfeickert]

Description

Add use citation from Evidence for B+→K+νν¯ Decays.

Congratulations to the Belle II collaboration on this excellent result!

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 'Evidence for B+→K+νν¯ Decays'.
   - c.f. https://inspirehep.net/literature/2725943
   - Congratulations to the Belle II collaboration on this excellent result!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (079356c) 98.28% compared to head (cc4440e) 98.28%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2393   +/-   ##
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  Coverage   98.28%   98.28%           
=======================================
  Files          69       69           
  Lines        4539     4539           
  Branches      803      803           
=======================================
  Hits         4461     4461           
  Misses         45       45           
  Partials       33       33           

Flag	Coverage Δ
contrib	97.86% <ø> (ø)
doctest	60.71% <ø> (ø)
unittests-3.10	96.29% <ø> (ø)
unittests-3.11	96.29% <ø> (ø)
unittests-3.8	96.32% <ø> (ø)
unittests-3.9	96.34% <ø> (ø)

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[matthewfeickert]

Relevant RTD build: https://pyhf--2393.org.readthedocs.build/en/2393/citations.html#use-in-publications