Update README to reference addBetaVersion helper (#1753)

* Update README to reference addBetaVersion helper

* Update README.md

README.md

@@ -253,13 +253,13 @@ To install a beta version of stripe-java follow steps [installation steps above]
 
 We highly recommend keeping an eye on when the beta feature you are interested in goes from beta to stable so that you can move from using a beta version of the SDK to the stable version.
 
-If your beta feature requires a `Stripe-Version` header to be sent, use the `Stripe.stripeVersion` field to set it:
+If your beta feature requires a `Stripe-Version` header to be sent, set the `Stripe.stripeVersion` field by calling `Stripe.addBetaVersion`:
 
 > **Note**
-> The `stripeVersion` can only be set in beta versions of the library.
+> Beta version headers can only be set in beta versions of the library.
 
 ```java
-Stripe.stripeVersion += "; feature_beta=v3";
+Stripe.addBetaVersion("feature_beta", "v3");
 ```
 
 ## Support