Nitpick: `ptl` may be better as `pl`
(Feel free to ignore.)
All the usage examples do import pytorch_lighting as ptl. Instead of ptl, pl may  be better as it doesn't clash with any library I know of, is 2 characters like NumPy's np, and is harder to mistype as plt, which many researchers probably also have imported. Since the library is in its early days, I don't think it would be that dramatic a change and is a little easier to read for people like me who often mix up letters like that.
On the other hand, it's pretty clear that it's not matplotlib from context, is yet another change, and is an aesthetic choice at its root, so it may not be worth it.