Add note about initializing a FileStream for async reading/writing

[sveinungf]

Hi, maybe this is worth mentioning. Basically, the FileOptions.Asynchronous flag should be passed when creating a FileStream (e.g. with File.Create), otherwise the actual I/O operations are performed synchronously. More info.

[davidfowl]

Good one! Even though FileStream is still a disaster when it comes to async IO

[yahorsi]

Same sockets?

[davidfowl]

Sockets are fine.