Yes.. the .plugincompendium file should go inside the Author folder where the other .plugin files typically go.
Author isn't so important unless you care what gets displayed to the user. Different values will be used depending on the circumstance. Let me explain how the config works...
There are 3 conditions..
1) User had manually installed plugins themselves. (there is no .plugincompendium file) In this case version & author are pulled from the .plugin file. The name is used for matching with LOTRO Interface. In all the instances that these did not initially match, I compiled into LPC a small mapping table so that most of the existing plugins will match up.
2) Upon updating or installing with LPC, if a .plugincompendium file exists in the installed zip, it will use this, and use the author or version from it.
3) Upon updating or installing an addon that DOES NOT contain a plugincompendium file, LPC will autogenerate one. In this instance the author and version are taken from the LOTRO Interface feed that LPC retrieves each time it is ran. Keep in mind though that the dependencies your plugin needs may be missing. Information on how to annotate the dependencies are on LPC's info page.
This brings up another point.. To work around different limitations in LOTRO's lua beta.. many authors have started including multiple .plugin files in one download (to use with loading / refreshing / etc). In order to prevent multiple entries from showing in LPC, the .plugincompendium file allows you to fill out a list of the .plugin files that your plugin uses to operate under the "Descriptors" tag.
Here is an example of one that has a lot going on..
<?xml version="1.0" encoding="utf-8"?>
<PluginConfig xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Name>Bevy o Bars</Name>