Description: Avoid multiple, costly round trips to any origin
Failure description: Page made 12 round-trips to 3 origins.
Help text: Consider using<link rel=preconnect> to set up early connections before an HTTP request is actually sent to the server. This will reduce multiple, costly round trips to any origin.

We had previously discussed suggesting <link rel=dns-prefetch> to pre-resolve DNS of a specific domain, but per @igrigorik if we're recommending preconnect, dns-prefetch is a no-op and we don't need to recommend both.

previously: #873