small fixes

fido2/Makefile

@@ -40,5 +40,5 @@ libsolo.a: $(OBJ)
 	$(CC) $^ $(INT_CFLAGS) $(ECC_CFLAGS) -c -o $@
 
 clean:
-	rm $(OBJ) libsolo.a
+	rm -f $(OBJ) libsolo.a
 

fido2/device.c

@@ -12,6 +12,8 @@
  * aren't what you want to keep, but are designed to be replaced
  * with some other platform specific implementation.
  * 
+ * For real examples, see the STM32L4 implementation and the PC implementation of device.c.
+ * 
 */
 #include <stdint.h>
 #include <stdlib.h>