doc: rewrite the book foreword

Signed-off-by: Julian Orth <ju.orth@gmail.com>

doc/book/src/Foreword.md

@@ -1,15 +1,29 @@
 # Preface
 
-This document describes the (i) Wayland architecture, (ii) Wayland model of
-operation and (iii) its library API. Also, the Wayland protocol specification is
-shown in the Appendix. This document is aimed primarily at Wayland developers
-and those looking to program with it; it does not cover application development.
+This document describes the Wayland architecture and Wayland model of operation.
+This document is aimed primarily at Wayland developers and those looking to
+program with it; it does not cover application development.
 
 There have been many contributors to this document and since this is only the
 first edition many errors are expected to be found. We appreciate corrections.
 
 Yours, the Wayland open-source community November 2012
 
+## Protocol Documentation
+
+This document does not describe the semantics of individual messages sent
+between compositors and clients. Consult the following documents to learn about
+concrete Wayland interfaces, requests, and events.
+
+- [wayland.xml] - The official documentation of the core protocol.
+- [wayland-protocols] - Standardized Wayland extension protocols.
+- [wayland.app] - A community-maintained website that renders these protocols,
+  and many more, as easily accessible HTML pages.
+
+[wayland.xml]: https://gitlab.freedesktop.org/wayland/wayland/-/blob/main/protocol/wayland.xml
+[wayland-protocols]: https://gitlab.freedesktop.org/wayland/wayland-protocols
+[wayland.app]: https://wayland.app
+
 ## Copyright
 
 Copyright © 2012 Kristian Høgsberg