Add missing NuGet config.

NuGet.config

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <!-- Ignore global configuration -->
+    <clear />
+    <!-- Here so the Visual Studio package manager won't default to the next feed below. -->
+    <add key="OrchardCoreCommercePreview" value="https://nuget.cloudsmith.io/orchardcore/commerce/v3/index.json" />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
+    <add key="OrchardCorePreview" value="https://nuget.cloudsmith.io/orchardcore/preview/v3/index.json" />
+  </packageSources>
+  <packageSourceMapping>
+    <packageSource key="nuget.org">
+      <package pattern="*" />
+      <!-- OrchardCore.Translations.All is on a separate repo and doesn't have a preview -->
+      <package pattern="OrchardCore.Translations.*" />
+    </packageSource>
+    <packageSource key="OrchardCoreCommercePreview">
+      <package pattern="OrchardCore.Commerce*" />
+    </packageSource>
+    <packageSource key="OrchardCorePreview">
+      <package pattern="OrchardCore*" />
+      <!-- OrchardCore theme packages -->
+      <package pattern="SafeMode" />
+      <package pattern="TheAgencyTheme" />
+      <package pattern="TheBlogTheme" />
+      <package pattern="TheComingSoonTheme" />
+      <package pattern="TheTheme" />
+      <package pattern="TheAdmin" />
+    </packageSource>
+  </packageSourceMapping>
+</configuration>