Posting here per instructions to do so before filing a bug on github:
All of the modules yml files in metricbeat/modules.d (version 8.6.0) have broken documentation links in the top-of file comment.
The links in the docs all point to https://www.elastic.co/guide/en/beats/metricbeat/main/[page].html where it appears that the current documentation is at https://www.elastic.co/guide/en/beats/metricbeat/**current**/[page].html