tools: usb: p9_fwd: wrap USBG shell command examples in literal code blocks

Stephen Rothwell reported htmldocs warning when merging usb tree:

Documentation/filesystems/9p.rst:99: ERROR: Unexpected indentation.

That's because Sphinx tries rendering p9_fwd.py output as a grid table
instead.

Wrap shell commands in "USBG Example" section in literal code blocks
to fix above warning and to be in line with rest of commands in the doc.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/linux-next/20240905184059.0f30ff9a@canb.auug.org.au/
Fixes: 673f0c3f ("tools: usb: p9_fwd: add usb gadget packet forwarder script")
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20240908113423.158352-1-bagasdotme@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/filesystems/9p.rst

@@ -86,11 +86,11 @@ When using the usbg transport, for now there is no native usb host
 service capable to handle the requests from the gadget driver. For
 this we have to use the extra python tool p9_fwd.py from tools/usb.
 
-Just start the 9pfs capable network server like diod/nfs-ganesha e.g.:
+Just start the 9pfs capable network server like diod/nfs-ganesha e.g.::
 
         $ diod -f -n -d 0 -S -l 0.0.0.0:9999 -e $PWD
 
-Optionaly scan your bus if there are more then one usbg gadgets to find their path:
+Optionaly scan your bus if there are more then one usbg gadgets to find their path::
 
         $ python $kernel_dir/tools/usb/p9_fwd.py list
 
@@ -99,7 +99,7 @@ Optionaly scan your bus if there are more then one usbg gadgets to find their pa
           2 |   67 | unknown          | unknown          | 1d6b:0109 | 2-1.1.2
           2 |   68 | unknown          | unknown          | 1d6b:0109 | 2-1.1.3
 
-Then start the python transport:
+Then start the python transport::
 
         $ python $kernel_dir/tools/usb/p9_fwd.py --path 2-1.1.2 connect -p 9999