welcome to the forum,
i had asked the same question and here is the answer.
https://forum.rclone.org/t/how-to-suggest-a-change-to-rclone-documentation/12384
for purge command
- log into github
- goto https://github.com/rclone/rclone/blob/master/docs/content/commands/rclone_purge.md
- click the pencil icon
- make your proposed changes