docs(faq): added bug with hero button rendering
docs(faq): added bug with hero button rendering

The icon in a hero button doesn't render in the middle of the circle when button rendered as a link. Reported as https://github.com/OfficeDev/Office-UI-Fabric/issues/346.

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andrewconnell/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,andikrueger/ng-officeuifabric,jjczopek/ng-officeuifabric,s-KaiNet/ng-officeuifabric,andikrueger/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,andrewconnell/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,s-KaiNet/ng-officeuifabric,andrewconnell/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,andikrueger/ng-officeuifabric,andrewconnell/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,johnmeilleur/ng-officeuifabric,andikrueger/ng-officeuifabric,johnmeilleur/ng-officeuifabric,jjczopek/ng-officeuifabric,jjczopek/ng-officeuifabric,jjczopek/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,s-KaiNet/ng-officeuifabric,jjczopek/ng-officeuifabric,johnmeilleur/ng-officeuifabric,andikrueger/ng-officeuifabric,andrewconnell/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,s-KaiNet/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,s-KaiNet/ng-officeuifabric