fix: relative link to the flashing guide (#30)

Co-authored-by: markrossington <[email protected]>

README.md

@@ -40,7 +40,7 @@ I offer no warranty, support or guarantees. Any changes to your 3D printer firmw
 
 ## Program new firmware onto printer (aka flashing)
 > **Warning**
-> `scripts/marlin_flash.py` is a work in progress, please don't use yet. Follow the manual guide here: [flashing.md](flashing.md)
+> `scripts/marlin_flash.py` is a work in progress, please don't use yet. Follow the manual guide here: [flashing.md](/flashing.md)
 
 <details><summary>Expand to see how the script should work</summary>