For what it is worth, I have put together a step by step guide on how to install Roon Web Controller on a Raspberry Pi running DietPi with a kiosk browser and the Roon Bridge software.
The Roon Web Controller design was very heavily influenced by the open source Logitech Media Player controller called Jivelite.
Roon Web Controller currently has library browser functionality. The “Add to Library”, “Add to Playlist” or “Manage Play Queue” functionality is not available in the Roon API, so those features are not implemented.
For the step by step guide, see this wiki article that I wrote and please feel free to provide feedback. Following these instructions installs the Roon Web Controller software, installs Chromium (version 60 - new enough to use all of the features), and installs the Roon bridge software.