Add migration guides to the nav menu

docs/en/Migration-Guides/Index.md

@@ -0,0 +1,4 @@
+# ABP Framework Migration Guides
+
+* [ABP Framework 3.3.x to 4.0 Migration Guide](Abp-4_0.md)
+

docs/en/docs-nav.json

@@ -998,6 +998,10 @@
         {
           "text": "Road Map",
           "path": "Road-Map.md"
+        },
+        {
+          "text": "Migration Guides",
+          "path": "Migration-Guides/Index.md"
         }
       ]
     },