show the user how to set the unit cell dims in the final MTZ

[DHekstra]

since the unit cell dimensions coming out of laue data processing are only loosely tied to reality, perhaps we can add a cell at the end of the tutorial showing the user how to edit the unit cell of the final mtz by hand. something along these lines:

import reciprocalspaceship as rs

ds=rs.read_mtz(your.mtz)
ds.cell=(79.4,79.4,37.84,90,90,90)
ds.write_mtz(new_name.mtz)

[PrinceWalnut]

As of this commit the user can override the unit cell during laue.optimize_indexing. I can certainly add this to the end of the tutorial though.

[DHekstra]

Thanks