Add back documentation on separate idle and read timeout

Closes #87

read.go

@@ -26,6 +26,11 @@ import (
 // Call CloseRead if you do not expect any data messages from the peer.
 //
 // Only one Reader may be open at a time.
+//
+// If you need a separate timeout on the Reader call and the Read itself,
+// use time.AfterFunc to cancel the context passed in.
+// See https://github.com/nhooyr/websocket/issues/87#issue-451703332
+// Most users should not need this.
 func (c *Conn) Reader(ctx context.Context) (MessageType, io.Reader, error) {
 	return c.reader(ctx)
 }