Updated text in the jumbotron container to reflect the Bootstrap 3 change from hero unit to jumbotron. (Wasn't sure if it should be 'a Jumbotron' or just 'Jumbotron' though...
* Defaults to no rounded corners and full width in the viewport
* When in a container, the jumbotron has extra padding and will have
rounded corners
* Updates default jumbotron example to show the full width default
display
Fixes#9759.