Add DocSearch suppport

[tesseralis]

Hi there!

Congrats on almost finishing the Korean translation of the React docs. Before releasing, we have one more task to do. We need to change the DocSearch API key . One of the maintainers needs to sign up for DocSearch in order to do this.

[taehwanno]

Thanks. I signed up. I will change the DocSearch API Key.

[hg-pyun]

I'll delegate it to @taehwanno . Thank you.