docs: updated to cache backend

docs/install-node.rst

@@ -74,6 +74,7 @@ Save configuration to virtualenv and activate environment::
   export LIBVIRT_URI=test:///default
   export AMQP_URI=amqp://cloud:password@$(hostname)/circle
   export HYPERVISOR_TYPE=test 
+  export CACHE_URI=pylibmc://$(hostname):11211/
   END
 
 Copy the libvrit bindings to the local virtualenv directory::
@@ -92,4 +93,4 @@ Copy the upstart scripts for celery services::
 Start celery daemons::
 
   $ sudo start vmcelery
-  $ sudo start netcelery
\ No newline at end of file
+  $ sudo start netcelery