add search scope (dotnet#34)

Author: mairaw

dotnet/docfx.json

@@ -57,6 +57,7 @@
       "author": "dotnet-bot",
       "uhfHeaderId": "MSDocsHeader-DotNet",
       "apiPlatform": "dotnet",
+      "searchScope": [".NET"],
       "feedback_system": "GitHub",
       "feedback_github_repo": "dotnet/docs",
       "feedback_product_url": "https://developercommunity.visualstudio.com/spaces/61/index.html"