Update README for Japanese i18n Team

[t-inu]

Updates the followings.

• I think it is a rule to insert a half-width space not only for English words but also for single alphabets and numbers, so change from "英単語" to "英数字"
• As for the English letters, there is no rule to make it half-width, so describe it.
• It is better to describe the full-width and half-width usage rules first, rather than describing whether to insert a space, so change the order.

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以下について更新します。

• 英単語だけでなく、単独のアルファベットや数字の場合も半角スペースを入れるルールだと思うため、「英単語」から「英数字」に変更する。
• 英字について、半角にする決まりが書かれていないので記載する。
• スペースを入れるかどうかの記載よりも、先に全角と半角の使用ルールを記載するほうがよいので、順番を入れ替える。

---

/assign @shu-mutou
/cc @atoato88

[codecov]

Codecov Report

Merging #6625 (ffd08c5) into master (15300bd) will not change coverage.
The diff coverage is n/a.

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  Hits         4536     4536           
  Misses       5813     5813           
  Partials      301      301           

[shu-mutou]

/lgtm
Thanks!!

[k8s-ci-robot]

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