be explicit about the GDB script to use

with this change the user doesn't need to set an [auto-load-safe-path]

[auto-load-safe-path]: https://sourceware.org/gdb/onlinedocs/gdb/Auto_002dloading-safe-path.html

debug.gdb

@@ -0,0 +1,21 @@
+target remote :3333
+
+# print demangled symbols by default
+set print asm-demangle on
+
+monitor arm semihosting enable
+
+# # send captured ITM to the file itm.fifo
+# # (the microcontroller SWO pin must be connected to the programmer SWO pin)
+# # 8000000 must match the core clock frequency
+# monitor tpiu config internal itm.fifo uart off 8000000
+
+# # OR: make the microcontroller SWO pin output compatible with UART (8N1)
+# # 2000000 is the frequency of the SWO pin
+# monitor tpiu config external uart off 8000000 2000000
+
+# # enable ITM port 0
+# monitor itm port 0 on
+
+load
+step