Improve documentation for Attribution

[mjherzog]

Within the ABCTK documentation, we should make a distinction between the features and functions that operate on ABOUT files and those that do not require ABOUT files - namely Attribution. This means that we should organized the documentation at a high level under either Attribution or ABOUT files. The attrib and transform commands would be under Attribution and the rest under ABOUT files.

We also need a much more detailed explanation of the content of the transform yaml files - this could just be a copy of the help text from the --help--format function. We do not want to required someone to install ABCTK just to understand how the transform can work.