docs: added a diagram about Openflow

Author: rodrigomelo9

docs/images/Makefile

@@ -0,0 +1,15 @@
+#!/usr/bin/make
+
+FILES  = $(wildcard *.dot)
+FILES := $(basename $(FILES))
+FILES := $(addsuffix .svg,$(FILES))
+
+ODIR = .
+
+vpath %.svg $(ODIR)
+
+%.svg: %.dot
+	@mkdir -p $(ODIR)
+	dot -Tsvg $< -o $(ODIR)/$@
+
+all: $(FILES)

docs/images/openflow.dot

@@ -0,0 +1,28 @@
+digraph openflow {
+  graph [ranksep=0.25];
+  node [shape = doublecircle];
+  node [shape = rectangle];
+  GHDL "ghdl-yosys-plugin" Yosys "nextpnr-ice40" "nextpnr-ecp5" icetime icepack iceprog eccpack;
+  node [shape = note ];
+  VHDL Verilog;
+  node [shape = box3d ];
+  ice40;
+  node [shape = oval];
+  "bit-ice40" [label=".bit"];
+  "bit-ecp5"  [label=".bit"];
+  VHDL                -> {GHDL "ghdl-yosys-plugin"};
+  GHDL                -> "ghdl-yosys-plugin";
+  "ghdl-yosys-plugin" -> Yosys;
+  Verilog             -> Yosys;
+  Yosys               -> ".json";
+  ".json"             -> {"nextpnr-ice40" "nextpnr-ecp5"};
+  "nextpnr-ice40"     -> ".asc";
+  "nextpnr-ecp5"      -> ".config";
+  ".asc"              -> {icetime icepack};
+  icepack             -> "bit-ice40";
+  "bit-ice40"         -> iceprog;
+  iceprog             -> ice40;
+  ".config"           -> eccpack;
+  eccpack             -> "bit-ecp5";
+  {rank = same; GHDL ; "ghdl-yosys-plugin"; Yosys;}
+}

docs/images/openflow.svg

@@ -94,6 +94,10 @@ Openflow
 
 Openflow is the combination of different Free/Libre and Open Source (FLOSS) tools:
 
+.. image:: images/openflow.svg
+   :width: 70%
+   :align: center
+
 * Yosys for synthesis, with ghdl-yosys-plugin for VHDL support.
 * nextpnr in its ice40 and ecp5 versions.
 * Projects icestorm and Trellis.