Add a "Download Data" tuto in the Quick Start documentation page

[marinebcht]

The way to download exemple data in the Quick Start seems to be a little bit confuse.

It will be interesting to have a clear protocol like in Cars :

After this, add some notes in cli_accuracy or cli_topo like Take care that the path_to_elev and path_to_mask point to existing data. If they come from the xDEM exemple, refer Quick Start page to download them.

[rhugonnet]

Good idea. For this, I think we need to put forward xdem.examples.available that lists all the files:

xdem/xdem/examples.py

Line 51 in 02fbd7d

available = list(_FILEPATHS_DATA.keys()) + list(_FILEPATHS_PROCESSED.keys())

Then, we can simply say that downloading happens under-the-hood when calling a given path with xdem.examples.get_path().

[rhugonnet]

Another issue to link when we add new example data: #635