Adding example for looking up all coupons for a product family

samples/coupons.rb

@@ -24,6 +24,9 @@
 # Lookup up existing coupon using the product_family_id and the coupon code
 coupon = Chargify::Subscription::Coupon.find_by_product_family_id_and_code(2,"10OFF")
 
+# Looking up all coupons for a product family
+coupons = Chargify::Coupon.find_all_by_product_family_id(12345)
+
 # Update coupon information
 coupon      = Chargify::Coupon.find_by_product_family_id_and_code(2,"10OFF")
 coupon.code = "FOO"
@@ -38,10 +41,10 @@
 coupon.usage
 #>> [{"name"=>"Product 1", "savings"=>0.0, "id"=>8, "signups"=>5, "revenue"=>0.0}, {"name"=>"Product 2", "savings"=>0.0, "id"=>9, "signups"=>0, "revenue"=>0.0}]
 
-#Apply coupon to subscription
+# Apply coupon to subscription
 subscription = Subscription.find_by_customer_reference('moklett')
 subscription.add_coupon('5OFF')
 
-#Remove coupon from subscription
+# Remove coupon from subscription
 subscription = Subscription.find_by_customer_reference('moklett')
-subscription.remove_coupon('50OFF')
+subscription.remove_coupon('50OFF')