xfs_quota: add missed options -D and -P into man page

xfs_quota: add missed options -D and -P into man page

There're two options in xfsprogs/quota/init.c:init() function, the -D
option is used to set a file to instead of /etc/projects, and the -P
option is used to set a file to instead of /etc/projid. I don't know
these two options when I write xfstests case xfs/133, because
there's no any information about them in xfs_quota and other related
man pages.

Document these options in the xfs_quota man page.

Reported-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Bill O'Donnell <billodo@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>