Update filtering-in-rest.md
Update filtering-in-rest.md

Added more information about filtering against country codes
ted-spence-avalara/developer-dot,bob-erdman/developer-dot,bob-erdman/developer-dot,ted-spence-avalara/developer-dot,bob-erdman/developer-dot,ted-spence-avalara/developer-dot,bob-erdman/developer-dot,ted-spence-avalara/developer-dot,ted-spence-avalara/developer-dot,bob-erdman/developer-dot