Maps: Add info on tile layers & fair use somewhere, allow to add own tile provider

[jancborchardt]

As far as I know, all the tile providers we have are kind of "fair use", that is if you have a big instance and use it a lot you should actually not use them and add your own tile provider. Right?

We should probably:

• Clarify this info about the tile servers and thank them somewhere
• Link how to add a custom Mapbox/other provider url for tile layer (we only have that for routing atm)
• Link an easy guide how to host your own tile server, probably with https://openmaptiles.org ?

What do you think @nextcloud/maps?

[eneiluj]

There is no way to easily add a tile layer for now. It's definitely a feature coming in further versions.

Yep about the tile server setup guidelines and yep about thanking the amazing public servers we use.