Move examples in classic commands closer to the top

[fricklerhandwerk]

Problem

Command line examples for classic commands are at the very bottom of each manual page, which makes them hard to discover after reams of generic options.

Proposal

Move them right after the description, as with the experimental commands.

Checklist

• checked latest Nix manual (source)
• checked open documentation issues and pull requests for possible duplicates

Priorities

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