Update ur.md

Author: shannona

_pages/ur.md

@@ -256,7 +256,8 @@ https://github.com/BlockchainCommons/Research/blob/master/papers/bcr-2020-006-ur
    * [**ur:seed Test Vectors**](/ur/vectors/seeds/)
 * [**A Guide to Using URs for PSBTs**](/ur/psbts/) [our biggest success story]
 * [**UR SSKRs & Envelope SSKRs**](/sskr/)
-* [List of UR Implementations](/ur/implementations/)
+* [**List of UR Implementations**](/ur/implementations/)
+* [**Known Values**](/known-values/)
 
 **Playground:**