<remarks> in doc comments don't show up in api docs

[halter73]

For example, the following remark that ShutdownTimout defaults to 5 seconds in KestrelServerOptions.cs doesn't show up in the generated api docs:

/// <summary>
/// The amount of time after the server begins shutting down before connections will be forcefully closed.
/// Kestrel will wait for the duration of the timeout for any ongoing request processing to complete before
/// terminating the connection. No new connections or requests will be accepted during this time.
/// </summary>
/// <remarks>
/// Defaults to 5 seconds.
/// </remarks>
public TimeSpan ShutdownTimeout { get; set; } = TimeSpan.FromSeconds(5);

@danroth27