Mention the node.js PPA.

Most users would probably have to install node.js from here, as
node.js is not included in Ubuntu 10.04 and looks to be rather old in
newer Ubuntu versions.

README

@@ -24,6 +24,10 @@ Installing from binaries
 Ubuntu: there is a PPA available for ngitcached packages:
 https://launchpad.net/~rohanpm/+archive/ngitcached
 
+It is also recommended to obtain node.js from this PPA:
+https://launchpad.net/~chris-lea/+archive/node.js
+
+  sudo apt-add-repository ppa:chris-lea/node.js
   sudo apt-add-repository ppa:rohanpm/ngitcached
   sudo apt-get update
   sudo apt-get install ngitcached