update README.md

README.md

@@ -44,7 +44,7 @@ The firmware is able to run on pretty much any ESP32 microcontroller though. But
     * DEBUG = 1 if you'd like some more verbose feedback sent to the serial terminal
     * USE_DISPLAY = 1 if you were using a board with a display connected
     * HAS_KEYBOARD = 1 if you were using a matrix keyboard connected to the microcontroller
-    * DEBUG_DISPLAY = 1 (in display.h) to receive some more verbose feedback from the display driver
+    * DEBUG_DISPLAY = 1 (in display.cpp) to receive some more verbose feedback from the display driver
 - hit the upload button
 - wait for the compilation and upload to complete; this may take a while due to the compilation time of the libraries involved