[x/tour] content: link to working and updated korean translation
[x/tour] content: link to working and updated korean translation

The korean translation we link to is offline due to the

  Go 1.9 is no longer available.

error; but even before that it was quite outdated (last re-deployment
was ~6 years ago).

A few people have been working on an updated translation, which they
deployed at go-tour-ko.appspot.com (repo github.com/golang-ko/tour).

I don't speak korean but I've skimmed through it and it looks fine.
Link to the new one.

Updates golang/tour#1026
Fixes golang/tour#709
Fixes golang/tour#1027

Change-Id: I08edb12737a82381aeb33bb3f324e87b92936115
Reviewed-on: https://go-review.googlesource.com/c/tour/+/253337
Reviewed-by: Alberto Donizetti <90b16103a35511ced020676f3544f17117fb4c92@gmail.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Trust: Alberto Donizetti <90b16103a35511ced020676f3544f17117fb4c92@gmail.com>
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
X-Tour-Commit: 6f9d4ff994b136951d420708cd231da267653086

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website