docs: Update ATLAS 3G tt 2L citation

[kratsg]

Pull Request Description

Citation initially referred to CONF note that's now superseded by the paper. Likely better to cite the paper on arXiv.

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• Tests are passing
• "WIP" removed from the title of the pull request
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* Update 3G tt 2L CONF note that is superseded by paper
   - c.f. https://inspirehep.net/literature/1844425

[codecov]

Codecov Report

Merging #1330 (913fbad) into master (efc0ae3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1330   +/-   ##
=======================================
  Coverage   97.50%   97.50%           
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  Files          63       63           
  Lines        3760     3760           
  Branches      538      538           
=======================================
  Hits         3666     3666           
  Misses         55       55           
  Partials       39       39           

Flag	Coverage Δ
unittests	97.50% <ø> (ø)

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[kratsg]

@matthewfeickert - why is this complaining? I got the citation from inspirehep.

[matthewfeickert]

Love it. 🚀