Improve docstring.

src/Stripe.net/Services/Topups/StripeTopupCreateOptions.cs

@@ -7,7 +7,7 @@ namespace Stripe
     public class StripeTopupCreateOptions : StripeBaseOptions
     {
         /// <summary>
-        /// A positive integer in the smallest currency unit (e.g., 100 cents to charge $1.00 or 100 to charge ¥100, a 0-decimal currency) representing how much to charge the card.
+        /// A positive integer in the smallest currency unit (e.g., 100 cents to top up $1.00 or 100 to top up ¥100, a 0-decimal currency) representing how much to top up your Stripe balance.
         /// </summary>
         [JsonProperty("amount")]
         public int? Amount { get; set; }