made openocd always use SWD and added small note about gdb debugging files

openocd tried "Info : auto-selecting first available session transport "jtag". To override use 'transport select <transport>'." using a JLink debugger. Overriding it with SWD is what I did. With the CMSIS debugger openocd you get lucky, by Info : auto-selecting first available session transport "swd".. Hope forcing it always to SWD will make it easier for others using different debuggers.

Documentation/debugger.rst

@@ -115,6 +115,12 @@ command to soft-reset card10.
    ...
    (gdb)
 
+.. note::
+   You will also find the following self-describing gdb files in the firmware
+   root directory, which do not require additional arguments:
+   ``flash-all.gdb,  flash-bootloader.gdb,  
+   flash-both.gdb,  flash-epicardium.gdb,  flash-pycardium.gdb``
+
 .. warning::
    If you are used to use ``mon reset halt``, be aware that the card10 prototypes
    do not connect the reset line to the debugger. OpenOCD is configured to only do