doc: note the EOF behaviour of read_until
@@ -23,6 +23,8 @@ cfg_io_util! {
///
/// If successful, this function will return the total number of bytes read.
///
+ /// If this function returns `Ok(0)`, the stream has reached EOF.
+ ///
/// # Errors
///
/// This function will ignore all instances of [`ErrorKind::Interrupted`] and
