Add a search bar for tikv.org docs

[ran-huang]

It's hard to locate a doc on tikv.org. Currently the only way is clone this repo and search locally.

[juzhiyuan]

How about integrating with https://www.algolia.com/ to support search online?

[juzhiyuan]

see https://www.algolia.com/products/search-and-discovery/hosted-search-api/

[ran-huang]

How about integrating with https://www.algolia.com/ to support search online?

That would be lovely!