index: add node.js section and express gcp backend

Front page link for #1050

Blocking on https://github.com/GoogleCloudPlatform/gcloud-node-todos/pull/19 and a deploy on gcloud-todos.appspot.com

/cc @viviancromwell @stephenplusplus @s3ththompson 
@proppy proppy and i discussed this on IM,  I don't think developers think of GCP or gcloud-node.  They think "oh i want to use x framework for front end" and 'use y on server side'. let me find some ORM solution , oh there is gcloud-node to bind for gcp....

I see this section is more full stack.....instead of 'backend"