Add some comments

Signed-off-by: Harsha Vamsi Kalluri <[email protected]>

server/src/main/java/org/opensearch/index/mapper/DateFieldMapper.java

@@ -568,6 +568,7 @@ public Relation isFieldWithinQuery(
             DateMathParser dateParser,
             QueryRewriteContext context
         ) throws IOException {
+            // if we have only doc_values enabled we do not look at the BKD so we return an INTERSECTS by default
             if (isSearchable() == false && hasDocValues()) {
                 return Relation.INTERSECTS;
             }