Show plugins README inline

I am just testing out grav for the first time to consider using for our company website (instead of wordpress). First of all, great job so far love the directions this is heading - making it a nice experience for developers as well as non-tech content authors.

I think it would be nice if the README file on the plugin info page (so e.g. `admin/plugins/star-ratings`) could be displayed inline. Would save a bit of time but could also make it a bit more nicer for the more non-tech people using grav and not necessarily knowing what github is, maybe being a bit more reluctant to click on that link (I am imagining this to be one of the comments if we where to start using grav right now from some of our team-members)