Add missing nuget case to system package provider docs

Author: jakepetroules

Sources/PackageDescription/PackageDescription.docc/Curation/SystemPackageProvider.md

@@ -4,6 +4,7 @@
 
 ### Providing Hints to Users of System Packages
 
-- ``brew(_:)``
 - ``apt(_:)``
+- ``brew(_:)``
+- ``nuget(_:)``
 - ``yum(_:)``