`SynchronizedCollection<T>.Add(T)` incorrectly references itself as "read-only"

The method [`SynchronizedCollection.Add(T)`](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.synchronizedcollection-1.add?view=net-8.0#system-collections-generic-synchronizedcollection-1-add(-0)) says in the description: "Adds an item to the thread-safe, **read-only** collection.", but the `SynchronizedCollection` is not read-only.

Note:
The [`Insert(Int32, T)`](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.synchronizedcollection-1.insert?view=net-8.0#system-collections-generic-synchronizedcollection-1-insert(system-int32-0))-Method simply talks from a collection:
> Inserts an item into the collection at a specified index.