Clarify non-native @jstype support for Java 16 records

Does not attempt to address native support - like enums, if this is to
be supported, it will likely require its own annotation and semantics.

Fixes google#6

java/jsinterop/annotations/JsType.java

@@ -28,7 +28,7 @@
  *
  * <p>Marking an object with JsType is similar to marking each public member of the class with
  * {@link JsProperty}/{@link JsMethod}/{@link JsConstructor} respectively. In order for this to work
- * correctly the JavaScript name needs to be unique for each member. Some unobvious ways to cause
+ * correctly the JavaScript name needs to be unique for each member. Some nonobvious ways to cause
  * name collisions are:
  *
  * <ul>
@@ -48,6 +48,9 @@
  * <p>For native interfaces with no particular JavaScript type associated with them (e.g. structural
  * types) it is recommended to use {@code namespace = JsPackage.GLOBAL} and {@code name = '?'}.
  *
+ * <p>If a Java {@code record} is marked a "non-native" JsType  public accessor methods are treated
+ * as though they are annotated with {@link JsProperty}.
+ *
  * <p><b>Instanceof and Castability:</b>
  *
  * <p>If the JsType is native, the generated code will try to mimic Javascript semantics.