Add docs to module-info.java (#1535)

Author: Degubi

gson/src/main/java/module-info.java

@@ -1,3 +1,7 @@
+/**
+ * Defines the Gson serialization/deserialization API.
+ * @since 2.8.6
+ */
 module com.google.gson {
 	exports com.google.gson;
 	exports com.google.gson.annotations;