Improve documentation for import_headings

[anirudnits]

• Resolves Add doc support for import_headings option #2111

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.22%. Comparing base (7b69d09) to head (98953df).
⚠️ Report is 275 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2113   +/-   ##
=======================================
  Coverage   99.22%   99.22%           
=======================================
  Files          38       38           
  Lines        3087     3087           
  Branches      747      747           
=======================================
  Hits         3063     3063           
  Misses         14       14           
  Partials       10       10           

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[DanielNoord]

Closing this as there are quite a lot of changes that don't make a lot of sense, such as changing __future__ to **future**. That makes it more effort to review the bits that do make sense.