Documentation of `optional` assumes left catch

[kl0tl]

The documentation for optional states that

optional empty = pure Nothing
optional (pure x) = pure (Just x)

but the second equation holds only for types satisfying the left catch law (pure a <|> b = pure a), like Aff, and not those satisfying the distributivity law ((f <*> a) <|> (g <*> a) = (f <|> g) <*> a), like Array.

We should at least remove the second equation but I find both equations helpful together to explain the behaviour of optional and I think its behaviour for types satisfying distributivity instead of left catch can be surprising at first (optional [x] = [Just x, Nothing] with Array for instance), so perhaps we should document both the left catch and distributivity behaviours?