Add further detail for PersistentQueue behaviour within .NET SDK documentation

The Data Model documentation for the .NET SDK is lacking detail in regards to describing the PersistentQueue behaviour. It describes it's use as a "lightweight job queue", which doesn't describe what the PersistentQueue implementation really is which is causing issues to arise:

We are looking for:

• Including that it is implemented as a shallow wrapper of the sub doc operations detailed here
• Implementation does not prevent duplicate elements per design similar to .NET's Queue<T> Class

Similarly there is no further information detailing it's behaviour in the following .NET SDK documentation:

Namespace Couchbase.DataStructures 3.4.13

Class PersistentQueue<TValue> 3.4.13 (couchbase.com) 

Interface IPersistentQueue<T> 3.4.13 (couchbase.com)