update placeholder name in comment

README.md

@@ -44,7 +44,7 @@ To build the EEPROM image, execute the following command.
 Pass any other configuration options you want to set to the first command or use `cmake-gui(1)`.
 
 ```shell
-# Replace <target> with one of the target architectures from the list above
+# Replace <arch> with one of the target architectures from the list above
 # This will default to at91sam3x8e (Arduino Due)
 cmake -DARCH=<arch> -B build -S .
 cmake --build build