CDK: add stb to navbar

Author: hsutaiyu

mkdocs.yml

@@ -89,6 +89,7 @@ nav:
       - Architecture:
         - CDK rollup: cdk/architecture/cdk-zkevm.md
         - CDK validium: cdk/architecture/cdk-validium.md
+        - Unified bridge - STB: cdk/architecture/staking-the-bridge.md
       - Specification:
         - Validium vs rollup: cdk/spec/validium-vs-rollup.md
       - Glossary: