SlnGen instructions are potentially incomplete (#1530)

Author: tg123

README.md

@@ -15,7 +15,7 @@ dotnet add package KubernetesClient
 ## Generate with Visual Studio
 
 ```
-dotnet msbuild /t:slngen
+dotnet msbuild /Restore /t:SlnGen kubernetes-client.proj
 ```
 
 ## Authentication/Configuration