Add wheelchairAccessibility enabled true to docs

[anthonyshull]

Summary

The example wheelchairAccessibility configs don't include "enabled": true, which is required for any other wheelchairAccessibility configurations to work. The docs are misleading without it as anyone copying them won't have wheelchair accessibility enabled.

[leonardehrenfried]

I'm going to repeat what I said on Gitter. This permanently enables wheelchair-routing for all requests which we don't want to suggest in the docs.

If you want you can update the docs to mention that you should switch it in the API.