[PubSub] Link in docs gives file not found

[see here](https://docs.dapr.io/developing-applications/sdks/dotnet/dotnet-messaging/dotnet-messaging-pubsub-howto/) - specifically the link from the following line is not found
```
Deploy a .NET Web API application ([StreamingSubscriptionExample](https://github.com/dapr/dotnet-sdk/tree/master/examples/Client/PublishSubscribe/StreamingSubscriptionExample))
```