opensnoop: update synopsis in man page
opensnoop: update synopsis in man page

tuxology/bcc,iovisor/bcc,brendangregg/bcc,brendangregg/bcc,tuxology/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,tuxology/bcc,brendangregg/bcc,brendangregg/bcc,tuxology/bcc,tuxology/bcc,iovisor/bcc