Added example Pmod config for amaranth on ULX3S board

See https://gist.github.com/opensiriusfox/755a3fa9967ebeaac0182c7a18b0727e

2023-10-07_blinky_led_ulx3s.py

@@ -0,0 +1,59 @@
+#!/usr/bin/env python3
+
+from amaranth import *
+from amaranth_boards.ulx3s import ULX3S_12F_Platform as ulx3s_tgt
+
+
+class LEDBlinker(Elaboratable):
+    """
+        LED Blinker reference code pulled directly from the Amaranth reference implemenetation
+        https://amaranth-lang.org/docs/amaranth/latest/start.html#a-blinking-led
+    """
+    def elaborate(self, platform):
+        m = Module()
+
+        led = platform.request("led")
+        # The following lines requests the platform give us a custom thing
+        # I've called `sf_led` which is a 4-pin PmodLED device.
+        led_pmod = platform.request("sf_led")
+
+
+        half_freq = int(platform.default_clk_frequency // 2)
+        timer = Signal(range(half_freq + 1), reset=0x00)
+
+        with m.If(timer == half_freq):
+            m.d.sync += led.eq(~led)
+            m.d.sync += timer.eq(0)
+        with m.Else():
+            m.d.sync += timer.eq(timer + 1)
+
+        # Just for visibility, make the four LEDs on the module toggle in step
+        # with the main LED. the top most will be aligned to the main LED,
+        # while the other three LEDs will be inverted
+        m.d.sync += led_pmod.bit_select(0,1).eq(led)
+        m.d.sync += led_pmod.bit_select(1,1).eq(~led)
+        m.d.sync += led_pmod.bit_select(2,1).eq(~led)
+        m.d.sync += led_pmod.bit_select(3,1).eq(~led)
+
+        return m
+
+
+from amaranth.build import Resource
+from amaranth.build import Pins
+
+# This last bit of code is for the synthesis step. We define the pin-collection
+# for the PMOD in the physical configuration we intend to use. I plugged in the
+# PMOD into the bottom row of connectors on the side of my ulx3s board, running
+# from the pins labeled 14 to the pin labeled 17.
+pin_set = Pins("14+ 15+ 16+ 17+", dir="o", invert=False, conn=("gpio", 0))
+# Next I indicate this is a resource that a module can request by name as `sf_led`
+# and indicate on my system it is pluged into the pin set
+sf_pmod_resource = Resource.family(0, default_name="sf_led", ios=[pin_set])
+
+# The "correct" way to do this is likely to define a custom configuration for
+# the hardware I'm using that inherits ULX3S_12F_Platform and further extends
+# the resources based upon my use of the pins.
+
+ULX3S = ulx3s_tgt()
+ULX3S.add_resources([sf_pmod_resource])
+ULX3S.build(LEDBlinker(), do_program=True)