Better documentation for simple_continued_fraction

[NAThompson]

Closes #970

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.41%. Comparing base (080a089) to head (d51f3c4).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1457      +/-   ##
===========================================
- Coverage    95.41%   95.41%   -0.01%     
===========================================
  Files          831      831              
  Lines        69588    69588              
===========================================
- Hits         66400    66399       -1     
- Misses        3188     3189       +1     

see 1 file with indirect coverage changes

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