doc: twister: fix argument order in custom flash example

Fixes sample command added to the documentation by commit
a31f784 ("twister: add a --flash-command flag")

During the review of #93944, I recommended to change the order and pass
user --flag(s) last. This was changed in the code but not in the example
added to the documentation.

Signed-off-by: Marc Herbert <[email protected]>

Author: marc-hb

doc/develop/test/twister.rst

@@ -1466,8 +1466,9 @@ in a hardware map.
          --device-serial COM1
          --flash-command 'custom_flash_script.py,--flag,"complex,argument"'
 
-Would result in calling ``./custom_flash_script.py --flag complex,argument --build-dir
-<build directory> --board-id <board identification>``.
+Would result in calling ``./custom_flash_script.py
+--build-dir <build directory> --board-id <board identification>
+--flag complex,argument``.
 
 Fixtures
 +++++++++