No error/feedback when livedown not installed

[agarzola]

I switched my default Node version with nvm and it took a while for me to realize that I needed to reinstall livedown globally, since nvm installs these global packages per-version of Node. Showing the user some kind of error message when livedown is not available would be helpful in figuring out why an installation that previously worked well suddenly stops working.

[ethagnawl]

This happens to me infrequently enough that I don't immediately remember that I need to install the Node plugin and frequently enough that I've found myself on this issue more than once.