add reference to Rule 9 when talking about API
add reference to Rule 9 when talking about API

karawoo/10-simple-rules-data-storage,snim2/10-simple-rules-data-storage,PBarmby/10-simple-rules-data-storage,naupaka/10-simple-rules-data-storage,jhollist/10-simple-rules-data-storage,emhart/10-simple-rules-data-storage,fmichonneau/10-simple-rules-data-storage