Add missing Javadocs.

Change-Id: I63f0086ed99a259391ef6094a5218744d4b2fc60
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
index c8bb310..066f709 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
@@ -32,6 +32,12 @@
   private final List<StructuredParameterProvider> parameterProviders;
   private final List<LabelProvider> labelProviders;
 
+  /**
+   * Constructs a {@link Formatter}.
+   *
+   * @param parameterProviders the {@link StructuredParameterProvider}s to apply to each log entry.
+   * @param labelProviders the {@link LabelProvider}s to apply to each log entry.
+   */
   public Formatter(
       Collection<StructuredParameterProvider> parameterProviders,
       Collection<LabelProvider> labelProviders) {