Update to r42809:

This patch:

• clarifies that this is an alternative to pkgng
• updates the listing version numbers and removes the example for manually fetching a pkg
• removes .tgz format
• does some word-smithing to make what is demonstrated clearer and to refer the reader to man pages for further usage examples
• comments out the author info so that it doesn't render in the print version

Reviewed by: bcr
Differential Revision: https://reviews.freebsd.org/D5375