SOLR-13452: Add comment on why kerby-pkix is excluded.
diff --git a/solr/core/build.gradle b/solr/core/build.gradle
index c6843e5..0cce7f8 100644
--- a/solr/core/build.gradle
+++ b/solr/core/build.gradle
@@ -211,7 +211,7 @@
 }
 
 unusedDeps {
-  jarExclude 'kerby-pkix-.*?\\.jar'
+  jarExclude 'kerby-pkix-.*?\\.jar' // used by security components dynamically
 }
 
 task runJavacc(type: org.apache.lucene.gradle.JavaCC) {