Add example about elm Tasks

[gabrielperales]

It's time to get started with elm Tasks. I've been learning elm for a while but I still have not worked with them yet, at least in my own code.

I guess they have to be something like javascript promises, but to have a deeper understanding about Tasks I want to see/do a straightforward example handling asynchronous operations.

[gabrielperales]

I found this medium post explaining some Tasks changes from version 0.17 to 0.18. In the other hand, the official documentation about Tasks is empty at the time of writing this comment, so there are not too many resources.

[gabrielperales]

I found also this post talking about how to chain some http requests with Task.andThen. I'm sure it can be helpful for understanding how Tasks works.