Fix defaults and README

This was meant to go into v6.5.0: default arguments and the README have been correctly updated. (Default gear/wheel levels are 23/13.)

Full Changelog: v6.5.0...v6.5.1

sha1sum results:
886caee012391d4f1db69516c675b15bfdac3ad0 FindAFactor-6.5.1-cp310-cp310-manylinux_2_35_x86_64.whl
966b8048e86c1782f1929dd556b175ad83364653 FindAFactor-6.5.1-cp312-cp312-manylinux_2_39_x86_64.whl
3c7ab38e241a875d79c35ffaafeb14ef39de9e5f FindAFactor-6.5.1-cp312-cp312-win_amd64.whl
8f6462a80eb6a5b49d007b441bed0d71679c25b7 FindAFactor-6.5.1-cp313-cp313-macosx_13_0_x86_64.whl
b5b3077aa17f011a4506e3eed36f65e514dc8e9d FindAFactor-6.5.1-cp313-cp313-macosx_14_0_arm64.whl
d6c54e5f27ce909807123dc9eb690099d34f32dc FindAFactor-6.5.1-cp313-cp313-macosx_15_0_arm64.whl
fc37aa0dd73dd30187e6fb3694ac06d85a82c0d1 FindAFactor-6.5.1-cp38-cp38-manylinux_2_31_x86_64.whl
463aa361720e93afd9b4fa2cf8eb23578b9c4a52 findafactor-6.5.1.tar.gz