Link to rustc guide

As proposed in https://github.com/rust-lang-nursery/rustc-guide/issues/239

diff --git a/src/doc/index.md b/src/doc/index.md
index 33ee76739c5b2c0ea7f0a55691fbcf7e3682971a..f702052e04937ae0ff9223fa942a954ca7ad5bd6 100644 (file)
--- a/src/doc/index.md
+++ b/src/doc/index.md
@@ -104,3 +104,9 @@ Rust. It's also sometimes called "the 'nomicon."
 ## The Unstable Book
 
 [The Unstable Book](unstable-book/index.html) has documentation for unstable features.
+
+## The `rustc` Contribution Guide
+
+[The `rustc` Guide](https://rust-lang-nursery.github.io/rustc-guide/) documents how
+the compiler works and how to contribute to it. This is useful if you want to build
+or modify the Rust compiler from source (e.g. to target something non-standard).