futility/cmd_gbb_utility.md: Add basic GBB subcmd doc

Sketch out the Markdown syntax required to generate
man page doc entries for futility sub-cmd's using
GBB as a motivating example.

BUG=b:298147229, b:298146304
TEST=pandoc cmd_gbb_utility.md -o output.html
BRANCH=none

Change-Id: I9066d655563998b923007a1461d81a21de49dac2
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/4699343
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Tested-by: Hsuan Ting Chen <roccochen@chromium.org>
Commit-Queue: Hsuan Ting Chen <roccochen@chromium.org>
1 file changed