Background:
This issue is part of the task to update the hook_help texts of the modules for Drupal 8:
#1908570: [meta] Update or create hook_help() texts for D8 core modules
Tasks:
- review if the text in filter_help() is up to date for Drupal 8
- test the links embedded in the text
- update d.o. docs at https://drupal.org/documentation/modules/filter