docs: Adjust how we approach author

[epage]

We've been getting questions like #5316 which shows that the discoverability of how to see that field is less than ideal. In fact, it only is talked about for the sake of version migration and for Command::author. Most derive users won't see that.

Steps

• Point derive users to help_template, like Command::author does
• Don't have useless author attributes that raise the question (rather than document it in the tutorial)

command! doesn't mention author, so I left it alone.