Clean up doc numbering

[jonathanbossenger]

Missed a few doc heading numbers in #117 so this is just a small clean up PR.

[github-actions]

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Co-authored-by: jonathanbossenger <psykro@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.59%. Comparing base (e510f3e) to head (32df841).
⚠️ Report is 1 commits behind head on trunk.

Additional details and impacted files

@@            Coverage Diff            @@
##              trunk     #125   +/-   ##
=========================================
  Coverage     90.59%   90.59%           
  Complexity      177      177           
=========================================
  Files            20       20           
  Lines          1489     1489           
  Branches        117      116    -1     
=========================================
  Hits           1349     1349           
  Misses          140      140           

Flag	Coverage Δ
javascript	94.20% <ø> (ø)
unit	89.57% <ø> (ø)

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[gziolo]

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