Link to persistence use from startup options page
Originally created by @BitingBird on #8998 (Redmine)
https://tails.boum.org/doc/first_steps/startup_options doesn’t mention persistence at all. We don’t want to duplicate doc, but it should link to https://tails.boum.org/doc/first_steps/persistence/use
Feature Branch: bitingbird:doc/8998-startup_persistence