Update the instructions for loading wifi drivers on FreeBSD versions
with or without devmatch. Mention that loading of drivers in
loader.conf or via rc.conf may be required for certain versions. It
should be done in order to have the lagg interface properly set up
at boot time.

Thanks to Pau Amma for providing the patch.
While here, fix some overly long lines in the note above.

PR: 246506 (documentation part)
Submitted by: pauamma_gundo.com
Requested by: cperciva (on IRC)
Reviewed by: cperciva, bcr
Approved by: bcr
Differential Revision: https://reviews.freebsd.org/D25881