AI: add section for building LLM powered applications Change-Id: Ifad2abaafc7120279d11dbda6a761948807b728a Reviewed-on: https://go-review.googlesource.com/c/wiki/+/621600 Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>