describe the "magic" behind align_on_AIRPORT

[espinielli]

Please document the magic behind .all("aligned_on_LSZH") whereby aligned_on_ils("LSZH") is invoked to each Flight in Traffic:

from traffic.data.datasets import landing_zurich_2019

landings = landing_zurich_2019.between("2019-10-15 10:10", "2019-10-15 10:50")
data = (
    landings
    .all("aligned_on_LSZH")
    .eval()
)

[xoolive]

Thank you, I will mark this as duplicate with #128