In Firebase Storage, select the file then copy the link address
In firebase realtime database, click on the + sign next to your node when you hover over it, type your friendly name in the Key and paste the link address as the Value. Press Add.
Ok, it has to be done manually, I supposed that can be automatically updated when a file has been uploaded...
I think that I have all information I need for going on with my project, your indications have been very helpful!! 
if only - Storage and Database are completely disconnected, even in the same project. You could probably do something using google apps script....