Update unsafe_routes guide to suggest ECMP configuration #310
Description
https://nebula.defined.net/docs/guides/unsafe_routes/ explains how to set up unsafe_routes for a nebula network.
slackhq/nebula#1332 added support for Equal-Cost Multi-Path routing by configuring multiple nebula hosts to route an unsafe route.
It'd be great to add this as a "for extra credit" section or as an additional note in the guide.