Update deploy-ubuntu.md and add javascript install instructions

doc/deploy-ubuntu.md

@@ -10,6 +10,7 @@ Deploy on Ubuntu 14.04
 5. Install [RabbitMQ](https://www.rabbitmq.com/)
 6. Install [Bitcoind](https://en.bitcoin.it/wiki/Bitcoind)
 7. Install [Nginx with Passenger](https://www.phusionpassenger.com/)
+8. Install a JavaScript Runtime
 8. Configure Peatio
 
 ### 1. Setup deploy user
@@ -139,7 +140,14 @@ find the following lines, and uncomment them:
     passenger_root /usr/lib/ruby/vendor_ruby/phusion_passenger/locations.ini;
     passenger_ruby /home/deploy/.rbenv/shims/ruby;
 
-#### 8. Setup production environment variable
+### 8. Install a JavaScript Runtime
+
+A JavaScript Runtime is needed for Asset Pipeline to work. Any runtime will do but Node.js is recommended.
+
+    sudo apt-get install nodejs
+
+
+#### 9. Setup production environment variable
 
     echo "export RAILS_ENV=production" >> ~/.bashrc