doc: update troubleshooting for Kconfig help

Fix the omission of having bullets for the enumeration of options, as
it makes the formatting look properly vs just different lines.

Change-Id: I701f705bc03ccc2082439c3ea3c1b5053b2aac0a
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>