Docs: Update translation for admin/index

trafficserver-doc-ja/trafficserver-doc-ja#22
https://docs.trafficserver.apache.org/en/latest/admin/index.en.html
[元の訳](https://github.com/trafficserver-doc-ja/trafficserver/pull/114/files#diff-2d4811de8446af1023bed16d08eb1c09L584) が悪いみたいですが、`Information is free, abundant, and accessible.` の訳がありません。