Link to the new relay lifecycle blog post if it's a new relay

Useful criteria for determining if it's a new relay would be:

• if the consensus weight is twenty
• if the first-seen is within the past week

We could consider adding a "new_relay" field to Onionoo, but this is simple enough that I'd be happy enough adding this to Atlas directly.

The new relay lifecycle blog post is at https://blog.torproject.org/lifecycle-new-relay.

When we move Atlas to the Metrics website, we can use the bootstrap alert classes to style this across the top of the Atlas details page.