add packageSourceMapping

Author: Bertk

NuGet.config

@@ -5,8 +5,20 @@
     <!-- Coverlet nightly build feed -->
     <add key="coverletNightly" value="https://pkgs.dev.azure.com/tonerdo/coverlet/_packaging/coverlet-nightly/nuget/v3/index.json" />
     <!-- dotnet-libraries feed -->
+    <!-- https://dev.azure.com/dnceng/public/_artifacts/feed/dotnet-libraries/NuGet/System.CommandLine/versions -->
     <add key="dotnet-libraries" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-libraries/nuget/v3/index.json" />
     <!-- Default nuget feed -->
-    <add key="nuget" value="https://api.nuget.org/v3/index.json" />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
 </packageSources>
+
+  <!-- Define mappings by adding package patterns beneath the target source. -->
+  <packageSourceMapping>
+    <!-- key value for <packageSource> should match key values from <packageSources> element -->
+    <packageSource key="nuget.org">
+      <package pattern="*" />
+    </packageSource>
+    <packageSource key="dotnet-libraries">
+      <package pattern="System.CommandLine" />
+    </packageSource>
+  </packageSourceMapping>
 </configuration>