Mettre à jour 'firmwares/marlin/README.md'

firmwares/marlin/README.md

@@ -45,4 +45,5 @@ I've done some update in their configuration :
 * I need moar `PROGMEM` and use [OctoPrint](https://octoprint.org/), `SDSUPPORT` is disabled , so i can comment back `DISABLE_M503`
 * Step/mm, PIDs are feeded from my own values.
 * `GRID_MAX_POINTS_X` & `GRID_MAX_POINTS_Y` are set to 5
+* enabled `G26_MESH_VALIDATION` for test purposes