net/url: document requirements for IPv6 addresses in URL.Host
When the host subcomponent of a URL is an IPv6 address, it must be
surrounded by square brackets to prevent colons in the address
from being interpreted as the port: "[fe80::1]:80".
Document this requirement.
Fixes #61093
Fixes #61276
Change-Id: Iaf411b9dc211fd876468d6e2e94ff672ba0d329d
Reviewed-on: https://go-review.googlesource.com/c/go/+/508976
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Joseph Tsai <joetsai@digital-static.net> Reviewed-by: Cherry Mui <cherryyz@google.com>