Read vector example

[curran]

Description

This adds a snippet to examples/search-knn.js that clarifies how one would read a vector back out of Redis after having stored it.

I had to do this myself in my app logic, after having gotten the vector similarity search basically working, as a means of checking whether a given vector had already been computed.

Closes #2566

Checklist

• Does npm test pass with this change (including linting)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?