update instructions for nightly builds (#1591)

Author: krwq

README.md

@@ -28,8 +28,8 @@ You can install the latest daily pre-release build of the .NET Core System.Devic
 ### NuGet.exe
 
 ```shell
-nuget install System.Device.Gpio -PreRelease -Source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json
-nuget install Iot.Device.Bindings -PreRelease -Source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json
+nuget install System.Device.Gpio -PreRelease -Source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet6/nuget/v3/index.json
+nuget install Iot.Device.Bindings -PreRelease -Source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet6/nuget/v3/index.json
 ```
 ### Official Build Status
 
@@ -38,8 +38,8 @@ nuget install Iot.Device.Bindings -PreRelease -Source https://pkgs.dev.azure.com
 ### .NET CLI
 
 ```shell
-dotnet add package System.Device.Gpio --source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json
-dotnet add package Iot.Device.Bindings --source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json
+dotnet add package System.Device.Gpio --source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet6/nuget/v3/index.json
+dotnet add package Iot.Device.Bindings --source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet6/nuget/v3/index.json
 ```
 
 ## Contributing