add introduction to book

README.md

@@ -10,8 +10,8 @@ UCG WG - Rust's Unsafe Code Guidelines Working Group
 
 The goal of the UCG WG is to produce the [Unsafe Code Guidelines
 Reference][ucg_book]: a "guide" for writing unsafe code that "recommends" what
-kinds of things unsafe code can and cannot do. It is largely a work-in-progress
-right now.
+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.
 
 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

reference/book.toml

@@ -1,5 +1,5 @@
 [book]
-authors = ["Niko Matsakis"]
+authors = ["UCG WG"]
 multilingual = false
 src = "src"
 title = "Unsafe Code Guidelines Reference"

reference/src/SUMMARY.md

@@ -1,7 +1,7 @@
 # Summary
 
-[Glossary](./glossary.md)
-
+- [Introduction](./introduction.md)
+- [Glossary](./glossary.md)
 - [Data layout](./layout.md)
   - [Structs and tuples](./layout/structs-and-tuples.md)
   - [Scalars](./layout/scalars.md)

reference/src/introduction.md

@@ -0,0 +1,14 @@
+## Rust's Unsafe Code Guidelines Reference
+
+This document is produced 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.
+
+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.
+
+[ucg_wg]: https://github.com/rust-lang/unsafe-code-guidelines
+[Rust Language Reference]: https://doc.rust-lang.org/reference/index.html