Update README.md

README.md

 x393
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-![x393 Block Diagram](x393_diagram.svg)
+![x393 Block Diagram](x393_diagram.png)
 
 FPGA code for Elphel 393 camera, created with [VDT plugin](https://github.com/Elphel/vdt-plugin). It runs on Xilinx Zynq 7030 SoC (FPGA plus dual ARM).