Update to r44908:

Describe that it's possible to install prebuilt binaries as well as build from source.
Instructions on how to extract distfiles on 8.x & earlier / 9.0 & later
Remove reference to jail_www_devfs_ruleset rc.conf, as-is it prevents the jail from starting because a ruleset needs to be defined & as there is no documentation for that in the article, it's easier to remove it, by doing this, the default ruleset is applied.
Add instructions on how to keep jails up to date with freebsd-update.

Reviewed by: bcr
Differential Revision: https://reviews.freebsd.org/D6050