libexec/inetd: Add -S to tftpd usage example in inetd.conf

[marck]

Summary

Since 273a307d0b80743fb08e23237b3f74dc94a8fa2a there is '-S' option which uses generic file permissions when tftpd is chrooted ('-s /chroot/dir') instead of special requirements "be publicly writable"

The '-s /tftproot' is always used in the usage example, so add '-S' here too

[eugen_grosbein.net]

Approved. You may commit this. Though, maybe use -S as first option to not mix lower and upper case options (sort them).

[marck]

In D49807#1142940, @eugen_grosbein.net wrote:

Though, maybe use -S as first option to not mix lower and upper case options (sort them).

In the man page, options are sorted case-insensitive (while, the order is reversed in options list but not in synopsis)