Acquisitions Admin updates

Updates to the chapter on acquisitions administration, including 1) the
reintroduction of the Providers section, which appears to have dropped out
of the docs after 2.1 2) the new default # copies and improvements to
distributions formulas introduced in 2.4 and 3) minor copy editing.

Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Signed-off-by: Dan Scott <dscott@laurentian.ca>