Render a block diagram of the xilinx_bitstream.ksy file into the Sphinx Docs

@kc8apf put together a [Kaitai Struct language](http://kaitai.io/#what-is-it) description of the Xilinx Bitstream format here -> https://github.com/SymbiFlow/prjxray/blob/master/docs/xilinx_bitstream.ksy

It would be great to render in our document as the file as shown here -> http://formats.kaitai.io/edid/index.html

KSY can be [converted to GraphViz .dot format](http://formats.kaitai.io/edid/graphviz.html). Sphinx has an [extension for rendering GraphViz files](http://www.sphinx-doc.org/en/master/ext/graphviz.html).

KSY can be [converted to Python code and Sphinx can read Python code](http://formats.kaitai.io/edid/python.html). That could be a useful method for getting the stuff into Sphinx too.