Docs: Give example for importing stat cats via Holdings Import Profile

This section of the docs needs a better example for the format of Stat Cat Data:

http://docs.evergreen-ils.org/reorg/dev/cataloging/_import_item_attributes.html

Here's how Galen explained it via email:
https://markmail.org/message/y3sra3tmbvwsceo7

When it says "CATEGORY" it's looking for the name of the Evergreen stat cat and for VALUE the label of the stat cat value you want to set. If (for the sake of argument), your stat cats are named "ARIS age range" and "ARIS format", the 949$w should contain something like this:

$w ARIS age range|Adult||ARIS format|E-book

Two pipes delimit each stat cat you want to set, while a single pipe separates the stat cat name and value. If you only want to set just one of the stat cats, the 949$w would be something like this:

$w ARIS format|E-book