README.md in paddle-2.1.3 vs README.md in paddle-2.1.4

@@ -31,10 +31,15 @@
   # Set the API version. Defaults to 1
   config.version = 1
 end
 ```
 
+### Caveats
+
+The Paddle API doesn't take `nil` values for optional parameters. If you want to
+remove a value, you'll need to pass `"null"` instead.
+
 ### Products
 
 ```ruby
 # List all products
 # https://developer.paddle.com/api-reference/products/list-products
@@ -117,9 +122,10 @@
 ```ruby
 # List all customers
 # https://developer.paddle.com/api-reference/customers/list-customers
 Paddle::Customer.list
 Paddle::Customer.list(status: "active")
+Paddle::Customer.list(email: "[e-mail]")
 
 # Create a customer
 # https://developer.paddle.com/api-reference/customers/create-customer
 Paddle::Customer.create(email: "[e-mail]", name: "Customer Name")