Documentation: i2c: add testunit docs to index

Fixes: a8335c64c5f0 ("i2c: add slave testunit driver")
Reported-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
1 file changed