Add note about ccExp setValidity vs real control
Add note about ccExp setValidity vs real control

Closes #22

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antoinepairet/angular-credit-cards,aspone/angular-credit-cards,SimeonC/angular-credit-cards,matiasarayac/angular-credit-cards,Noxwille/angular-credit-cards,bendrucker/angular-credit-cards,dingels35/angular-credit-cards,dribehance/angular-credit-cards,robertbaker/angular-credit-cards