docs: add nodejs-legacy package

npm won't work without it
"This package contains a symlink for legacy Node.js code requiring
binary to be /usr/bin/node (not /usr/bin/nodejs as provided in Debian)."

docs/deploy.rst

@@ -35,7 +35,7 @@ Update the package lists, and install the required system software::
   sudo apt-get update
   sudo apt-get install --yes virtualenvwrapper postgresql git \
     python-pip rabbitmq-server libpq-dev python-dev ntp memcached \
-    libmemcached-dev gettext wget pwgen nginx npm
+    libmemcached-dev gettext wget pwgen nginx npm nodejs-legacy
   sudo npm -g install bower less yuglify
 
 Set up *PostgreSQL* to listen on localhost and restart it::

docs/install.rst

@@ -61,7 +61,7 @@ Update the package lists, and install the required system software::
   sudo apt-get update
   sudo apt-get install --yes virtualenvwrapper postgresql git \
     python-pip rabbitmq-server libpq-dev python-dev ntp memcached \
-    libmemcached-dev npm
+    libmemcached-dev npm nodejs-legacy
   sudo npm -g install bower less yuglify
 
 Set up *PostgreSQL* to listen on localhost and restart it::