Some text for the tutorial.
Fix typo.
Be explicit about what's required and what's not.
Progress on tutorial text.
Fix the bridge tutorial to use the Exodus bridge.

... instead of a yet-to-be-created VTK bridge.
There are still some gaps, such as a missing
implementation of the BridgeExodusIOJSON class.
Merge topic 'bridge-tut'

b7bedb62 Fix the bridge tutorial to use the Exodus bridge.
5a974390 Progress on tutorial text.
2fe521db Be explicit about what's required and what's not.
847db7dd Fix typo.
0d1bf2a7 Some text for the tutorial.