Sometimes devices don't appear and it can be confusing. Add a few notes to
help with this situation.
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: fix 2 issues in the doc and include the doc in the index.rst]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
