(#22533) Provide instructions for finding routes.yaml

This patch provides a way for users to find the path to `routes.yaml`.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #664 from kbarber/docs/1.3.x/22533-routes-full-path-in-docs

Docs/1.3.x/22533 routes full path in docs