Bring this section up to reality.

(1) Additional __FreeBSD_version's from <osreldate.h>. Closes PR

docs/1438.

Submitted by: "David E. O'Brien" <obrien@Nuxi.cs.ucdavis.edu>

(2) Make it clear that when submitting a port, the package is not

necassary.

Suggested by: joerg

(3) Recommend people to use send-pr to send us notifications of new

ports and upgrades so that they won't fall between the cracks.

Suggested by: a lot of people

(4) Add a section about Motif and describe REQUIRES_MOTIF and

MOTIFLIB.

Prodded by: chuckr

(5) Revise the licensing problems section and describe the two

variables RESTRICTED and NO_CDROM.

(6) Fill in the section about upgrading. In particular, recommend to

send in diffs of the old and new ports (these are "ports", not the
original source or anything!), so it's easier to see what has
changed.