seq.1: reset option list alignment + tag spdx

[ziaee]

Summary

This buys us two lines at MANWIDTH 80 and three at 59.

MFC after: 3 days

[mhorne]

This is the general rule/convention for utility option lists? If so that is the point most worth noting in the commit message.

Approved.

[ziaee]

Yes, style.mdoc(5) says "in case the longest item is too long and hurts readability, the reccomendattion is to set the -width argument to indent". I wasn't sure how to put that in the msg.