DOC: Add base SVG file for the "figure1" (aka the workflow) flowchart

I have taken a stab at mapping the whiteboard scribbles of our sprint into an SVG file.

I've realized of several things I will go over in our weekly meeting (in 30 min aprox):

- *dMRIPrep* SHOULD NOT concatenate runs (#43)
- SDC (fieldmaps) requires transferring almost all responsibilities over to *SDCFlows* - that includes some of the issues that @mattcieslak raised within #43.
- We need to reconsider where denoising should be inserted (and listen what @jelleveraart has to say about this). The question is would denoising help have a better estimation of head motion and/or Eddy deformations?

Hopefully, this will help us progress faster towards our roadmap.

Resolves: #5