Document new 2.5 feature in Acq docs

This commit adds documentation in two places for the new Acq feature
"Opportunistic Acquisitions In-Process Copy Overlay". First, a short
note is added to the "Load MARC Order Records" doc. Second, the feature
is described more thoroughly in the "Batch Importing MARC Records" doc.
Also, this commit cleans up a hard-coded ordered list and a few small
wording and formatting problems.

Signed-off-by: Remington Steed <rjs7@calvin.edu>
Docs: Reformat numbered lists into AsciiDoc syntax

This commit improves list formatting in the Batch Importing section by
converting various hard-coded numbered lists into AsciiDoc syntax. Where
images are included, those are forced to be inline by adding a '+' to the
preceeding line. And whitespace was removed from the end of two lines. No
other changes are included.

Signed-off-by: Remington Steed <rjs7@calvin.edu>