Add example of getting wind speeds at turbines

[paulf81]

Yes

Feature or improvement description
This adds a new example file that demonstrates two ways of getting the wind speeds at each turbine

Related issue, if one exists
Issue #422

[Bartdoekemeijer]

The example looks good to me. I just wonder whether we need this to be a separate example. Perhaps we can include this in an existing example, or just limit it to the documentation?

[paulf81]

Maybe a separate example for now (so we have something) and then one day this is all in the documentation? What do you think @rafmudaf and @bayc ? I had the impression the new documentation is a big lift and will take some time?

[paulf81]

Thanks @bayc !