Bug#807810: Mention what if one wants to mark the bug forwarded to more than one place

[積丹尼 Dan Jacobson]

Package: devscripts
Version: 2.15.9
Severity: wishlist
File: /usr/share/man/man1/bts.1.gz

       forwarded bug address
           Mark the bug as forwarded to the given address (usually an email
           address or a URL for an upstream bug tracker).

Mention what if one wants to mark the bug forwarded to more than one place.