Clarify "the new" in dependent function types
Clarify "the new" in dependent function types

(also added missing `val`)
I was skimming over at this documentation and it actually took me a while to notice what is new.
So I added the comment to clarify. 
It is also possible to write `type EntryToKey = (e: Entry) => e.Key` and use it instead to clarify this is a dependent type
lampepfl/dotty,lampepfl/dotty,dotty-staging/dotty,som-snytt/dotty,som-snytt/dotty,lampepfl/dotty,lampepfl/dotty,som-snytt/dotty,dotty-staging/dotty,sjrd/dotty,lampepfl/dotty,som-snytt/dotty,sjrd/dotty,sjrd/dotty,som-snytt/dotty,sjrd/dotty,dotty-staging/dotty,dotty-staging/dotty,dotty-staging/dotty,sjrd/dotty