Update README to include Discussion about the flow of files through the Rodeo

[jeremyf]

Within the context of the DerivativeRodeo we have conceptual data structures associated with the file set.

• Chute: What are the files we’re bringing to the rodeo
• Agenda: What files are the rodeo responsible for making
• RoundUp: What files do we actually have when all is done; what we will associate with the corresponding FileSet.

The DerivativeRodeo is responsible for making the files required by the Agenda that are not in the Chute (e.g. Agenda - Chute). The RoundUp is the Agenda ∪ Chute;

Related to:

• Conditional Derivatives: Inject module into registered to override function utk-hyku#343
• EPIC: Import Optimization with Out of Band Processing adventist_knapsack#421
• Change date issued and periodical adventist-dl#3

[jeremyf]

This has been done through numerous commits.