Fix handbook section 4.5

[RobotsOnDrugs]

https://www.freebsd.org/doc/handbook/ports-using.html

Using ports is different in HBSD, and some of the instructions seem outdated, even for upstream.

[birlorg]

I started on this before I saw this issue @ birlorg@88843c1

@RobotsOnDrugs are you still doing this?

[RobotsOnDrugs]

@birlorg
I've been away from HBSD for a while because of other things in my life. Feel free to take ownership.

[birlorg]

k, I put in #7 that at least gets ports installed for users.