This patch does the following:
- Change the warning message to remove the reference to a specific PF version and point out that FreeBSDs pf has diverged from what's in OpenBSD.
- Remove a link to the old pf porting efforts, which are obsolete nowadays and don't provide much value to the reader anymore
- Change the flow in reading to put the ALTQ section at the end of the chapter. Most people don't use ALTQ with PF, so having that at the end of the chapter is good to not overwhelm the reader too much with concepts they probably don't need.
- Remove the "In order to" sentence parts which are mostly superfluous and can be replaced with "to" to increase readability
- Sprinkle in some sysrc in examples where it makes sense to use it