docs(aio): Add link to Japanese localization

[lacolaco]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the new behavior?

Added a link to https://angular.jp , Japanese localized aio.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

The below contents are translated

• index.html
• features
• quickstart
• tutorial
• glossary
• cheatsheet

[lacolaco]

Any blockers?

[lacolaco]

Our https://angular.jp is not completed localization but well-maintained and up-to-date.
It has 1600+ visitors per week. It is already used by many Japanese people.

I hope angular-l10n project is still alive...
cc/ @ocombe

[sandangel]

@lacolaco I just want to say thanks to you and the team. I'm working in Japan now and I really don't know how to explain some angular term to my Japanese colleges. Not many Japanese could use English or willing to learn it, and I was really happy when find out your site and give it to my team. I owe you one and hope could meet you in person at ng-japan conf in June. ^^

[gkalpak]

For some reason this is consistently failing on Travis, because it gets an old node.js version 😕

[lacolaco]

Should I rebase to master?

[lacolaco]

@gkalpak system all green!

[lacolaco]

I'm really happy, and proud of joining the Angular platform! Thank you!

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