Add robots.txt to limit Google crawler to English documents

[bahmutov]

Currently because of the way we have partially completed translations from English to Chinese and Japanese docs, Google text search can find English text on a Japanese page, leading to less optimal result.

We should add robots.txt to limit the Google crawler from indexing non-English translations for now

[jennifer-shehane]

I feel like implementing some of these best practices is more ideal than just completely ignoring translated files from search indexing. https://support.google.com/webmasters/answer/189077?hl=en&visit_id=637002396938016733-1976776371&rd=1

[bahmutov]

Sure, implementing the SEO optimizations for translations could be step 2

[jennifer-shehane]

yeah, I was convinced also of this in the standup. I made a not of it in the translation optimizations #1686