update deployed book introduction

Author: RalfJung

reference/src/introduction.md

@@ -1,14 +1,12 @@
 ## Rust's Unsafe Code Guidelines Reference
 
-This document is produced by the [UCG WG][ucg_wg] to provide a "guide" for
+This document is a past effort by the [UCG WG][ucg_wg] to provide a "guide" for
 writing unsafe code that "recommends" what kinds of things unsafe code can and
 cannot do, and that documents which guarantees unsafe code may rely on. It is
-largely a work-in-progress right now.
+largely abandoned right now. However, the [glossary](glossary.md) is actively
+maintained.
 
-Unless we state otherwise, the information in the guide is mostly a
-"recommendation" and still subject to change. The main goal for the WG in 2019
-is to RFC parts of the guide into the language specification, and move those
-parts into the [Rust Language Reference] proper.
+Unless stated otherwise, the information in the guide is mostly a
+"recommendation" and still subject to change.
 
 [ucg_wg]: https://github.com/rust-lang/unsafe-code-guidelines
-[Rust Language Reference]: https://doc.rust-lang.org/reference/index.html