A nice one line description of the project followed by badges when valuable and relevant.
A succinct paragraph that elaborates on the one line description. This should tell readers what the project has accomplished thus far or is aiming to accomplish.
Relevant information you need to know before you navigate. More context will then be provide by the component specific readmes. This is how the top level readme is taking the place of a wiki/delegator.
Describe who to contact for more information and what needs to be done.