README: slightly improve layout
README: slightly improve layout

- move badges on top
- put CI status in a table
OGRECave/ogre,paroj/ogre,OGRECave/ogre,paroj/ogre,OGRECave/ogre,paroj/ogre,paroj/ogre,paroj/ogre,OGRECave/ogre,OGRECave/ogre