Invalid link to custom-fields documentation
On the index.php?q=civicrm/admin/custom/group&reset=1 screen, the "learn more..." link appears to be broken -- this target of this link is currently https://docs.civicrm.org/user/en/latest/organising-your-data/custom-fields but should instead be https://docs.civicrm.org/user/en/latest/organising-your-data/creating-custom-fields/.
Using CiviCRM 5.1.1.