Processing pipelines metadata and figures

[dbirman]

We should fill out the processing.md file with more information about how processing pipelines are organized/built as well as some of the diagrams that are being built right now for how pipelines work.

Feel free to re-assign or break down into smaller tickets as needed.

[arielleleon]

@dbirman - can this be closed since we are working on diagrams in other tickets? #76