Documentation: Use file paths to flashing firmware tutorial

In preperation for CB:62424, replace HTTP links pointing to the flashing
firmware tutorial with file paths to the Markdown files.

Change-Id: I6a271a912348cbe002bc9cced9922ed743e1133c
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62452
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Thomas Heijligen <src@posteo.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>

0 files changed, 0 insertions, 0 deletions