release.7: update for current context

It's no longer unusual to be able to build a release with a single
command, so drop "actually" that hints at a surprise. Also just use
"network install directory" instead of referencing FTP; it's more
likely to be HTTP now.

Reviewed by: gjb
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D26260