improve documentation of LatticeVectors input parameter

In case both LatticeVectors and LatticeParameters are defined, we should clarify how the unit cell is constructed by Octopus. A couple of questions which I can’t find explicit answers for in the documentation:

1. Does LatticeVectors need to be normalized by the user?
2. Does LatticeVectors change the size of unit cell parameters defined by LatticeParameters?

Also, the tutorial is not correct on this: “LatticeVectors defines the direction of the vectors, while LatticeParameters defines their length.” From that statement I expect the the answers to the questions above to be

1. No
2. No

which is apparently not the case!