I’ve just pushed a small JavaScript change which makes it very easy to refer to any GraphHopper based application in a contact web site.
If you want to start a route with a fixed location do this via
https://graphhopper.com/maps/?point=berlin
If you want that the user can navigate to your location do this via an empty start point
https://graphhopper.com/maps/?point=&point=berlin
The same is also possible with ‘raw’ coordinates:
https://graphhopper.com/maps/?point=&point=52.519851%2C13.38727
I have included this in the documentation linking to a simple html form example.