[SEARCH] Improves kkn docs based on SEO guidelines (#2773)

## Description

This PR optimizes the content of the `kNN search` page based on the SEO
best practices outlined
[here](https://stunning-adventure-qrvr1k2.pages.github.io/style-guide/seo/).

---------

Co-authored-by: Liam Thompson <[email protected]>

Author: szabosteve