Method 1 (recommended):
Search for Rdio in Plex Online, within the Plex desktop app.
Method 2:
Download the latest package, unzip it, and place Rdio.bundle in ~/Library/Application Support/Plex Media Server/Plug-ins
Method 3:
Run the following commands.
cd ~/Library/Application Support/Plex Media Server/Plug-ins
git clone https://github.com/mikedecaro/Rdio.bundle.git
Version 1.0.2
Fixed a login issue caused by Rdio updating their login page.
Fixed an issue with logging in as a free account.
Version 1.0.1
Fixed an issue with maintaining log in.
Change single song selection to play the next track when finished.
Version 1.0.0
Fixed issue causing incorrect track names to be displayed.
Cleaned up logging.