Add guide for finding orbital transfer utility

The structure of chap 4.5 may not be sufficient for new users to find the utility they need, as this page was designed when we only had "starting from fch" approach but now we have "starting from fch/pyscf/mkl/molden".

It may be hard to draw a 2D figure to describe all the possible routes between programs. Instead, we can add a guide in a few words to remind the users that we have four approaches, starting from fch/pyscf/mkl/molden.