Add Specification link to Get Started menu

Author: bendichter

config/_default/menus.yaml

@@ -16,6 +16,10 @@ main:
     weight: 3
     url: "https://nwb-overview.readthedocs.io"
     parent: "Get Started"
+  - name: "Specification"
+    weight: 4
+    url: "https://nwb-schema.readthedocs.io/en/latest/format.html"
+    parent: "Get Started"
 
   # Software & Tools
   - name: "Software & Tools"