Fix docs and add iQIYI to the company list

OK, I see. But I still can't understand why development documents are not put in the docs directory.

The advantage of wiki is that it doesn't need to make a new commit, I think. Then why not make it a staging area of the docs directory, and only put things like design drafts there? Once it's stable, we can put it in the docs directory, and give users and developer a consist place to read the docs.

In fact, the vagrant development guide is [already](https://mesosphere.github.io/marathon/docs/developing-marathon-in-vagrant.html) in the docs directory.