Add examples for *PipeServerStream creation with PipeSecurity (ACLs)

It might be good to add examples that explain how to specify the [PipeSecurity](https://docs.microsoft.com/en-us/dotnet/api/system.io.pipes.pipesecurity?view=netcore-3.0)
(ACL) in a [NamedPipeServerStream](https://docs.microsoft.com/en-us/dotnet/api/system.io.pipes.namedpipeserverstream?view=netcore-3.0) and in an [AnonymourPipeServerStream](https://docs.microsoft.com/en-us/dotnet/api/system.io.pipes.anonymouspipeserverstream?view=netcore-3.0). We have usage examples on how to created *PipeServerStream objects, but nothing related to ACLs.

I found a simple example here that could inspire ours: https://weblogs.asp.net/gunnarpeipman/writing-simple-named-pipes-server-in-c

Just one important thing to keep in mind: that example sets the ACL _after_ the creation of the NamedPipeServerStream.

I am currently working on [this issue,](https://github.com/dotnet/corefx/issues/41657) which will add a new extension method that will set the PipeSecurity at the moment when the NamedPipeServerStream is created ([PR here](https://github.com/dotnet/corefx/pull/41838)). When the time comes, I will make sure the documentation for this new API will have a usage example so the user can set ACL at the moment of the pipe creation.

CC @mairaw @JeremyKuhne

Inizia trovando gli esempi di utilizzo esistenti di NamedPipeServerStream e AnonymousPipeServerStream nella documentazione di riferimento dell’API, quindi esamina la documentazione collegata di PipeSecurity e il lavoro correlato sull’API. Il lavoro è completato quando entrambi gli esempi di server-stream spiegano come configurare gli ACL, incluso il caso di configurazione al momento della creazione descritto nell’issue.

Scritto dal modello di indicizzazione a partire dal testo della issue.