Update Website Documentation

[zwimer]

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About a year ago #551 was merged which corrected incorrect documentation. This change has yet to be reflected on the website's documentation: https://digint.ch/btrbk/doc/btrbk.conf.5.html

Unless there is a reason to wait, like the next version update, it would be nice to update the website docs as the current options default|<Number> are quite different from yes|no; which at least for me caused a good bit of headache until I found this year-old issue.