[DOC] Beutify the chapter 'sahara on ironic'
[DOC] Beutify the chapter 'sahara on ironic'

There is a chapter 'know limitations:' in the home-page,
but I think it should belong to chapter 'sahara on ironic'.
So I replace the first level heading with second level heading
to beutify the home page.

And also replace 'do' with 'to' in title.

Change-Id: I73c46d00326750b8f26177d4ca46ebf9dbb611a7

tellesnobrega/sahara,openstack/sahara,tellesnobrega/sahara,egafford/sahara,egafford/sahara,openstack/sahara