[DOC] Adding sections to paper

[adam2392]

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PR Description

Closes: #83

Also fixes: #86

cc: @TomDonoghue

Merge checklist

Maintainer, please confirm the following before merging:

• All comments resolved
• This is not your own PR
• All CIs are happy
• PR title starts with [MRG]
• whats_new.rst is updated
• PR description includes phrase "closes <#issue-number>"

[codecov]

Codecov Report

Merging #87 (66ec859) into main (c0ddd1e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #87   +/-   ##
=======================================
  Coverage   86.90%   86.90%           
=======================================
  Files          22       22           
  Lines         863      863           
  Branches      104      104           
=======================================
  Hits          750      750           
  Misses         84       84           
  Partials       29       29           

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[adam2392]

Rendered docs will be here: https://circleci.com/gh/mne-tools/mne-icalabel/562?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

[adam2392]

https://output.circle-artifacts.com/output/job/c1c5314e-dfc5-4c60-9d70-b49a9b6cdc2c/artifacts/0/dev/api.html

[adam2392]

Kay once this is merged, I think the JOSS reviews will be addressed. Lmk if you have any final touches to add @mscheltienne @jacobf18 @anandsaini024