Add search feature

[mattstratton]

We should have the ability to search the site; probably add a search icon/field to the nav.

This is probably best achieved with google site search, etc.

[mattstratton]

The ideal setup is probably going to be using https://www.algolia.com/, but this will require us to create a json file to import.

Hugo .20 will allow us to create custom file types, so once this is released, we can likely implement this in a more robust manner.

[mattstratton]

Here's a bit of how hugo themselves have done it, so I don't forget:

https://github.com/spf13/hugo/pull/2016/files

My theory is that we can use the node client and upload the index on all builds, provided it's not very slow...

[bridgetkromhout]

How Algolia search was implemented for the Helm site: helm/helm-www#194