Unclear or missing information in the section periodic cleanup tasks

[stoamandl]

If you follow the instructions on https://docs.joinmastodon.org and run the installation as described here https://docs.joinmastodon.org/admin/install you will think that the instructions are related to Ubuntu. But then in this section https://docs.joinmastodon.org/admin/setup/#cleanup should be described that CRON jobs under Ubuntu must be specified with $PATH variants. Otherwise the cron jobs will not work. Of course this can be different for each system or Docker. For Ubuntu 20.04 should work with PATH=/home/mastodon/.rbenv/shims:/usr/bin

[aaaaalbert]

This issue appears to have a suggested fix here: #824.

(cc: @vmstan)

[stoamandl]

fixed in #824