Add missing link in TOC

Author: rbrundritt

articles/azure-maps/toc.yml

@@ -247,6 +247,8 @@
       href: https://docs.microsoft.com/javascript/api/azure-maps-drawing-tools/
     - name: Service module
       href: https://docs.microsoft.com/javascript/api/azure-maps-rest/
+    - name: Spatial IO module
+      href: https://docs.microsoft.com/javascript/api/azure-maps-spatial-io/
   - name: Resource Manager template
     href: /azure/templates/microsoft.maps/accounts
 - name: Resources