Course re-run section and refs to it in others

@explorerleslie, @talbs please check for accuracy and completeness
@WatsonEmily please circulate to PMs for level of detail, other likely questions to address, format
@mhoeber , @srpearce please consider this a developmental/copy edit
@sarina, @nasthagiri if you have time I value your input also!

If it's simpler, you can just state that if the user has permissions to rerun a course, then the Rerun button will appear in Studio. And then list the required permissions.  Otherwise, it sounds as if the user needs to take time and action to explicitly verify the 3 conditions above.