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

added newline at end of file

ignoring platformio folders.

.gitignore

@@ -4,4 +4,8 @@
 *.DS_Store
 *.d
 
+.pio
+.vscode
+
 README.md
+

platformio.ini

@@ -0,0 +1,9 @@
+[platformio]
+src_dir=grbl
+
+[env:uno]
+platform=atmelavr
+board=uno
+framework=arduino
+
+monitor_speed=115200