Update description to add leaflet layers (from providers) to the map

[arunge]

• There seems to be two types of leaflet maps, "maps" (1, 3) and "layers" (2, 4). "Layers" can be added or be removed, one can check or un-check them. Please, let us discuss if we could add a new option here.

  

originally from https://github.com/Pandora-IsoMemo/iso-app/issues/161#issuecomment-1576554944

[arunge]

As discussed, I will only update the description and mention that the user should only use maps (dot symbol) and not layers (checkbox symbol) here.

[arunge]

On iso-app beta in the tab "interactive map" the description for adding a new map type was updated to:

How to select a new map:

1. Select a map from https://leaflet-extras.github.io/leaflet-providers/preview/ and copy the name.
2. Delete the input of the field 'Map type'.
3. Paste the name of the map into the field 'Map type'.
4. Click 'Add...', and the custom map will be selected.

Some maps are not supported, e.g. those that are selectable via a checkbox, and not via a radion button. Please try maps from e.g. following providers 'OpenStreetMap', 'Stamen', 'Esri', 'CartoDB', 'NASAGIBS', 'GeoportailFrance'.