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 
Not sure we want this. For example, we don't have logos from the other examples/frameworks and if we start accepting, our page could look a little cluttered.