Add title margin for articles

[minsoochoo0122_proton.me]

Summary

Unlike books, FreeBSD articles don't have margin between the title and the site header. For example, this book's title, "The Design and Implementation of the 4.4BSD Operating System", has top margin between the header. Whereas in this article, you can see that the title "A project model for the FreeBSD Project" does not have its top margin, and therefore, the title is too close to the header. I'm adding top margin of 0.8 rem like book pages have.

Test Plan

bmake run