Adding missing javadoc

Signed-off-by: Ankit Jain <akjain@amazon.com>

lucene/core/src/java/org/apache/lucene/search/PointRangeQuery.java

@@ -240,6 +240,9 @@ public abstract class PointRangeQuery extends Query {
     }
   }
 
+  /**
+   * Weight implementation used by Point Range Query
+   */
   public static class PRQWeightImpl extends ConstantScoreWeight {
     private final PRQConfig config;
     private final ScoreMode scoreMode;