Update README.md

Added note on using `byte[]` in variables (see #163)

Author: rose-a

README.md

@@ -43,6 +43,8 @@ var heroAndFriendsRequest = new GraphQLRequest {
 };
 ```
 
+Be careful when using `byte[]` in your variables object, as most JSON serializers will treat that as binary data! If you really need to send a *list of bytes* with a `byte[]` as a source, then convert it to a `List<byte>` first, which will tell the serializer to output a list of numbers instead of a base64-encoded string.
+
 ### Execute Query/Mutation:
 ```csharp
 var graphQLClient = new GraphQLHttpClient("https://swapi.apis.guru/");
@@ -62,6 +64,8 @@ var graphQLResponse = await graphQLClient.SendQueryAsync<HeroAndFriendsResponse>
 var heroName = graphQLResponse.Data.Hero.Name;
 ```
 
+
+
 ### Use Subscriptions
 
 ```csharp