Update to r41052:

First pass at this chapter. This patch addresses the following:

&os;, you, and please
fix xref, acronym, and directory tags (still needs ulink review)
removed redundant warning, leaving only first instance; this warning can be removed altogether once 7.x is EOL at end of month

Reviewed by: bcr
Differential Revision: https://reviews.freebsd.org/D4726