Fix XML example in README for IntegerExplicitValueModification

Changed uppercase 'IntegerExplicitValueModification' to lowercase 'integerExplicitValueModification' in the README example to match the correct XML parsing requirements.

Fixes #214

Author: Claude Assistant

README.md

@@ -271,9 +271,9 @@ We can of course use this concept by constructing our TLS workflows. Imagine you
             <Heartbeat>
                 <payloadLength>
                     <modifications>
-                        <IntegerExplicitValueModification>
+                        <integerExplicitValueModification>
                             <explicitValue>20000</explicitValue>
-                        </IntegerExplicitValueModification>
+                        </integerExplicitValueModification>
                     </modifications>
                 </payloadLength>
             </Heartbeat>