How do I create or modify a custom filter? I'm following the docs here to create a custom filter.

The first sentence says: 


  Go to Custom Filters (/admin/settings/customfilter) (6.x &amp; 7.x)


However, that link just redirects me to the overall admin menu page (looks the same as if I go to /admin). What am I doing wrong?
Did you install the Custom Filters module? (https://www.drupal.org/project/customfilter)

Works fine for me after I install the module.