Mention validation in the README (#6640)

Author: martinbonnin

README.md

@@ -27,7 +27,7 @@ Apollo Kotlin is a strongly typed GraphQL client that generates Kotlin models fo
 
 Apollo Kotlin executes operations against a GraphQL server and returns results as operation-specific Kotlin types. This means you don't have to deal with parsing JSON, or passing around `Map`s and making clients cast values to the right type manually. You also don't have to write model types yourself, because these are generated from the GraphQL definitions your app uses.
 
-Because generated types are operation-specific, you can only access data that you actually specify as part of an operation. If you don't ask for a particular field in an operation, you can't access the corresponding property on the returned data structure.
+Because generated types are operation-specific and validated against the schema, you can only access data that you actually specify as part of an operation. If you don't ask for a particular field in an operation, you can't access the corresponding property on the returned data structure.
 
 This library is designed with Android in mind, but you can use it in any Kotlin application, including KMP ([Kotlin Multi Platform](https://kotlinlang.org/docs/multiplatform.html)).
 

docs/source/index.mdx

@@ -10,7 +10,7 @@ description: Discover Apollo Kotlin, a robust GraphQL client for JVM, Android, a
 
 Apollo Kotlin executes operations against a GraphQL server and returns results as operation-specific Kotlin types. This means you don't have to deal with parsing JSON, or passing around `Map`s and making clients cast values to the right type manually. You also don't have to write model types yourself, because these are generated from the GraphQL definitions your app uses.
 
-Because generated types are operation-specific, you can only access data that you actually specify as part of an operation. If you don't ask for a particular field in an operation, you can't access the corresponding property on the returned data structure.
+Because generated types are operation-specific and validated against the schema, you can only access data that you actually specify as part of an operation. If you don't ask for a particular field in an operation, you can't access the corresponding property on the returned data structure.
 
 This library is designed with Android in mind, but you can use it in any Kotlin application, including KMP ([Kotlin Multi Platform](https://kotlinlang.org/docs/multiplatform.html)).