Add system/unique_board_id (#25)

Co-authored-by: Luke Wren <wren6991@gmail.com>

system/unique_board_id/CMakeLists.txt

@@ -0,0 +1,14 @@
+add_executable(unique_board_id
+        unique_board_id.c
+        )
+
+target_link_libraries(unique_board_id
+        pico_stdlib
+        pico_unique_id
+        )
+
+# create map/bin/hex file etc.
+pico_add_extra_outputs(unique_board_id)
+
+# add url via pico_set_program_url
+example_auto_set_url(unique_board_id)