UPSTREAM: doc: Add intro to the home page

The intro text is converted from wiki home page.

(cherry picked from commit 3239be535d16b10881513c0e97500cbd110426ab)

Original-Change-Id: I2bf0d8a3b2e16c9bb7e6fbde5931ff816aede14a
Original-Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/75723
Original-Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Original-Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
GitOrigin-RevId: 3239be535d16b10881513c0e97500cbd110426ab
Change-Id: Ic1e6ea48eb9cc42b5fe446441aa37dcf0a81d6da
Signed-off-by: CopyBot <copybot.service@gmail.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/flashrom/+/4605119
Commit-Queue: Edward O'Callaghan <quasisec@chromium.org>
Tested-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>