Clarification of DM.InitSpin in the manual

[Roberto Robles]

For the wishlist:

A user has drawn to my attention that the explanation of DM.InitSpin might be ambiguous. As stated in the wikipedia page (https://en.wikipedia.org/wiki/Spherical_coordinate_system) there are different competing definitions of angles theta and phi. Although SIESTA assumes the most common convention used in physics, it won't harm to make it unambiguous in the manual, changing from:

"...the spin direction may be specified for each atom by the polar angles theta and phi..."

to

"...the spin direction may be specified for each atom by the polar angle theta and the azimuthal angle phi..."

I would say this would be clear enough, but it would be even clearer adding the direction of the examples, i.e., the direction for atom 5 in the example is the x axis.