router sharding

@pmorie - started a branch for the router sharding document.  The intent is to put this into the `routing.md` after it is defined.  
Basically routers are nodes.  They have health checks.  They might be external or internal.  An ops team should configure a router implementation, then register it with OpenShift.  I don't know that we need more than that because we have tools for managing everything else (ie when we have sharded services, we'll be able to autoscale shards, and then autorebalance the routes bound to that shard).