It is more common to call the top level document index.rst. This is
what this patch is doing, along with all required references fixup.
(From yocto-docs rev: 2cea7fbba9210479fc0387d7e1b80da9885558f0)
Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>