doc/openocd.texi: add SWD to the transports supported by jlink

Since 67332532194b16b99f0535a41b4179ca5df349b0 jlink adapter driver
supports SWD in addition to JTAG.

Change-Id: I9376aa02d9281f3e2734d8f127cd42162633d95b
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2324
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>