Fix repo init/copy documentation

[Mr-Pi]

Please fix or remove https://rustic.cli.rs/docs/commands/misc/deduplication.html

The correct approach for rustic seems to be rustic copy --init and to use a config file like https://github.com/rustic-rs/rustic/blob/main/config/copy_example.toml .

[aawsome]

Thanks a lot for opening the issue @Mr-Pi ! The documention in fact needs some rework.
I fixed this deduplication issues in #26

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