wpb-22590: update mkdocs for wiab-stag page

Author: mohitrajain

mkdocs.yml

@@ -14,6 +14,7 @@ nav:
       - Version requirements: how-to/install/version-requirements.md
       - Dependencies on operator’s machine: how-to/install/dependencies.md
       - How to install Wire in a box (Demo): how-to/install/demo-wiab.md
+      - How to install Wire in a box (Staging): how-to/install/wiab-stag.md
       - Introduction: how-to/install/prod-intro.md
       - How to install kubernetes and databases: how-to/install/ansible-VMs.md
       - How to configure AWS services: how-to/install/aws-prod.md