Add parameter explanations for `Affine`, `AffineGrid` and others

[yiheng-wang-nv]

So far, there are no explanation for the parameter: shear and scale in Affine, AffineGrid, create_shear and create_scale. Users may not know what is shear, what is scale.

In addition, I suggest to add value ranges for all parameters belong to Affine, thus users can understand what kind of values can be input.

[Nic-Ma]

Sure, I will update the related docs and highlight reasonable input values.

Thanks.