Admin settings for Disallow NSFW Content and Content Warning are confusing

Followup for https://github.com/LemmyNet/lemmy-ui/pull/3899#issuecomment-3943951427. - On admin page, clicking "disallow nsfw content" hides the content warning input. But after reloading the page, the content warning field is shown again. Makes it unclear what the current state is. - It is also not entirely clear what each of these settings does, would be good to add a description for each. - In fact all settings could benefit from descriptions.