UPDATING: Show plural syntax for PORTS_MODULES

Show two examples in PORTS_MODULES to demonstrate space separation.
This also shows off our working PRIME dual-gpu support.
Switching to this doubled my laptop's battery life!

MFC after: 3 days
Reviewed by: mhorne
Approved by: mhorne (mentor)
Differential Revision: https://reviews.freebsd.org/D48342