Add documentation on specifying repositories for default reviewers.
Add documentation on specifying repositories for default reviewers.

Khan/reviewboard,atagar/ReviewBoard,bkochendorfer/reviewboard,chazy/reviewboard,davidt/reviewboard,davidt/reviewboard,custode/reviewboard,atagar/ReviewBoard,chazy/reviewboard,atagar/ReviewBoard,brennie/reviewboard,KnowNo/reviewboard,brennie/reviewboard,reviewboard/reviewboard,custode/reviewboard,atagar/ReviewBoard,1tush/reviewboard,KnowNo/reviewboard,bkochendorfer/reviewboard,1tush/reviewboard,atagar/ReviewBoard,bkochendorfer/reviewboard,1tush/reviewboard,custode/reviewboard,chazy/reviewboard,davidt/reviewboard,chazy/reviewboard,custode/reviewboard,sgallagher/reviewboard,chazy/reviewboard,Khan/reviewboard,brennie/reviewboard,beol/reviewboard,Khan/reviewboard,brennie/reviewboard,Khan/reviewboard,chipx86/reviewboard,1tush/reviewboard,sgallagher/reviewboard,chazy/reviewboard,chazy/reviewboard,1tush/reviewboard,1tush/reviewboard,KnowNo/reviewboard,atagar/ReviewBoard,Khan/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,1tush/reviewboard,1tush/reviewboard,atagar/ReviewBoard,reviewboard/reviewboard,chazy/reviewboard,atagar/ReviewBoard,sgallagher/reviewboard,beol/reviewboard,beol/reviewboard,Khan/reviewboard,Khan/reviewboard,chazy/reviewboard,KnowNo/reviewboard,reviewboard/reviewboard,beol/reviewboard,davidt/reviewboard,Khan/reviewboard,bkochendorfer/reviewboard,atagar/ReviewBoard,chipx86/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,Khan/reviewboard,1tush/reviewboard