Update to r40998:

Initial content fix. This patch addresses the following:

missing &os; entities
rewording to address you, we, and general redundancy
adds missing directory tags
replaces portupgrade with portmaster
replaces old version examples with 9.x and 1998 names with 2013
makes up-to-date consistent

While here, complete r47710.

Reviewed by: bcr
Differential Revision: https://reviews.freebsd.org/D4661