extend Readme.md for making DEM.tif

[bollegijscoding]

The Readme file now refers to the USGS website to download dem files, which (1) currently appears to be broken (probably is temporal), and (2) does not allow scripted download. Similar data can be downloaded from NASA Earth observation website which does allow scripted downloading.

Detailed Description

Downloading SRTM data from the USGS website requires at some point a significant number of manual work (https://earthexplorer.usgs.gov/). After logging in to the NASA Earth observation website, it is possible to make a list of *.hgt which can afterwards be downloaded with a script.

I believe this information can be useful for people (like me) who are trying to get up to speed with the code. If relevant, I would like to propose some changes to the README.md and provide some example code on how to download the *.hgt files and convert them to *.tif files.

Kind regards,

Tomas

[JackKelly]

Thank you for your comment!

We'd be very keen to receive a pull request which updates the README - thank you!

But please not that nowcasting_dataset is deprecated in favour of ocf_datapipes. (Sorry that's not documented - I'll state the deprecation in the README now)