docs: leds: index.rst: add a missing file

Changeset 26a07553 ("docs: ABI: sysfs-class-led-trigger-pattern: remove hw_pattern duplication")
didn't include the needed changes at index.rst.

Fixes: 26a07553 ("docs: ABI: sysfs-class-led-trigger-pattern: remove hw_pattern duplication")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/36a6e3aef6e57ea349f1b47c7731d4cd1e03ca77.1604312590.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>