AI: new wiki page

This is a start at adding some information about using AI services from Go.

Change-Id: I90d6c2ff959df2f3d62afde70ed5105f128bbc03
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/588895
Reviewed-by: Eli Bendersky <eliben@google.com>
Commit-Queue: Ian Lance Taylor <iant@golang.org>