Add platform.io that builds a file for Arduino uno. Its output exactly matches what Arduino IDE creates.

positron96 · positron96 · commit e53ecff7b7cf · 2020-09-22T12:46:16.000+07:00
diff --git a/platformio.ini b/platformio.ini
@@ -0,0 +1,9 @@
+[platformio]
+src_dir=grbl
+
+[env:uno]
+platform=atmelavr
+board=uno
+framework=arduino
+
+monitor_speed=115200
