feature: add legend explaining color gradient for radar imagery

[b9AcE]

It could be useful to have a map legend (explanation of colors/symbols) in the app, for the radar map. The colors are of course the ones listed below the map https://www.smhi.se/vadret/nederbord-molnighet/radar-blixt and the one symbol is the red cross for lightning listed below the colors.

To not get in the way of the actual map display, this information could instead be listed in the "Settings" category, as that is where documentation-like tabs such as "About app" and "Libraries" already exist and the user may therefore reasonably expect to find other documentation there if needed.

[sphrak]

Hi again, Yes, a legend is something I do have in mind so thank for you reporting this. It will be scheduled for 1.2.0.

Sincerely, Niclas

[ashwinvis]

A timestamp would also be nice for practical purposes.