Merge pull request #9436 from MaxWang-MS/add_move_banner

Add a we've moved banner to doc site

Author: polar-kev

scripts/docs/templates/mrtk/partials/navbar.tmpl.partial

@@ -23,4 +23,12 @@
       </form>
     </div>
   </div>
-</nav>
+</nav>
+  <div class="navbar alert-navbar">
+  <div class="container">
+      <div class="alert-navbar-message">
+        <h5>We've moved!</h5>
+        <p>Starting from MRTK 2.6, we are publishing both conceptual docs and API references on docs.microsoft.com. For conceptual docs, please visit <a href="https://docs.microsoft.com/windows/mixed-reality/mrtk-unity/">our new landing page</a>. For API references, please visit <a href="https://docs.microsoft.com/dotnet/api/microsoft.mixedreality.toolkit">the MRTK-Unity section of the dot net API explorer</a>. Existing content will remain here but will not be updated further.</p>
+    </div>
+  </div>
+  </div>