Fix breadcrumbs (dotnet#9406)

Author: raprice

breadcrumb/toc.yml

@@ -1,2 +1,7 @@
-- name: Docs
-  tocHref: /
+- name: .NET
+  tocHref: /dotnet/
+  topicHref: /dotnet/index
+  items:
+  - name: API browser
+    tocHref: /dotnet/api/
+    topicHref: /dotnet/api/index

docfx.json

@@ -40,6 +40,7 @@
     "externalReference": [],
     "globalMetadata": {
       "breadcrumb_path": "/dotnet/breadcrumb/toc.json",
+      "extendBreadcrumb": false,
       "recommendations": true,
       "author": "dotnet-bot",
       "ms.author": "dotnetcontent",