docs: add some jldoctest's

[oameye]

Checklist

Thank you for contributing to GraphCombinatorics.jl! Please make sure you have finished the following tasks before finishing the PR.

• Appropriate tests were added and tested locally by running: make test.
• Any code changes should be julia formatted by running: make format.
• All documents (in docs/ folder) related to code changes were updated and able to build locally by running: make docs.

Request for a review after you have completed all the tasks. If you have not finished them all, you can also open a Draft Pull Request to let the others know this on-going work.

Description

add some jldoctest's

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.09%. Comparing base (a38b384) to head (d2558b7).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #14   +/-   ##
=======================================
  Coverage   97.09%   97.09%           
=======================================
  Files           6        6           
  Lines         172      172           
=======================================
  Hits          167      167           
  Misses          5        5           

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