updates to README.md

[neuronflow]

We need:

• a short general description, what ereg is, what it can do and why it exists.
• the documentation needs to show how to modify/structure the configuration file
• the documentation needs to show how to transform images based on the derived registration matrixes.

[sarthakpati]

the documentation needs to show how to transform images based on the derived registration matrixes.

This is handled by the transform_file, and I have put this information in the main README:

Specifically, the wording reads: the transform file to save the transform to; if already present, will use this transform instead of computing a new one

[neuronflow]

Should we provide a register and a transform function/method to be more in line with other registration packages?

[sarthakpati]

Should we provide a register and a transform function/method to be more in line with other registration packages?

We already have that in the OO interface:

• register function
• resample function (this is the terminology used in the ITK world for applying the transform to an image)