Simple-rfsoc-4x2-Example Documentation

Reference firmware and software example for the RealDigital RFSoC 4x2 evaluation board (Xilinx Zynq UltraScale+ RFSoC, FPGA part xczu48dr-ffvg1517-2-e). Built on the SLAC axi-soc-ultra-plus-core platform; shared workflow documentation lives on the platform docs site.