Added examples/ top-level directory

examples/basys3/README

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+
+A simple example design, based on the Digilent BASYS3 board
+===========================================================
+
+This example uses Yosys for synthesis and Xilinx Vivado
+for place&route and bit-stream creation.
+
+Running Yosys:
+  yosys run_yosys.ys
+
+Running Vivado:
+  vivado -nolog -nojournal -mode batch -source run_vivado.tcl
+
+Programming board:
+  vivado -nolog -nojournal -mode batch -source run_prog.tcl
+
+All of the above:
+  bash run.sh
+