MFC r290260,r290262:

r290260:

Document undocumented long options for -t cd9660

Note which options have been implemented and which options haven't
been implemented

Submitted as the following NetBSD PRs: bin/50390 and bin/50392

Sponsored by: EMC / Isilon Storage Division

r290262:

Fix spelling of isolevel cd9660 option

Sponsored by: EMC / Isilon Storage Division