Add note about sorting to documentation (and possibly a transform function)

Continuing from #157 - sorting algorithms are available in vector-algorithm, but it isn't easy to find that information out, depending on how you search. For example, the Stackage Hoogle query for sort :: Ord a => Vector a -> Vector a doesn't come up with the result (because that package doesn't provide a wrapper for immutable vectors).

It would be nice if a note about this could be added to the top-level module Data.Vector, which serves as the "information hub" right now. Something along the lines of:

Note: Sorting algorithms for mutable vectors are available in the vector-algorithms package. If you want to sort an immutable vector, you can use the freeze and thaw functions to wrap calls to sorting functions of your choice.

Personally, I think it would be nice to have a helper function alongside

Data.Vector.Generic.transform 
  :: (PrimMonad m, Vector v a) 
  => (Mutable v (PrimState m) a -> m (Mutable v (PrimState m) a)) 
  -> v a
  -> m (v a)
transform f = unsafeFreeze <=< f <=< thaw

as an counterpart to Data.Vector.Generic.Mutable.transform (the signatures aren't exactly analogous though because of the extra m 🙁), but of course, it isn't strictly necessary, just a nice to have thing.

Inizia con il modulo Data.Vector di primo livello e verifica in che modo la relativa documentazione rimanda a vector-algorithms e alle API correlate. Aggiungi una nota che spieghi dove si trovano le funzioni di ordinamento mutable e come freeze/thaw possano supportare i vettori immutabili. Tratta separatamente l’helper di trasformazione immutable proposto, confrontandolo con Data.Vector.Generic.transform e Data.Vector.Generic.Mutable.transform prima di decidere se rientra nell’ambito.