Rollup merge of #57746 - mark-i-m:patch-2, r=Centril

Update README.md

Point contributors to the rustc-guide...

r? @steveklabnik

README.md

@@ -13,9 +13,13 @@ Read ["Installation"] from [The Book].
 ["Installation"]: https://doc.rust-lang.org/book/ch01-01-installation.html
 [The Book]: https://doc.rust-lang.org/book/index.html
 
-## Building from Source
+## Installing from Source
 [building-from-source]: #building-from-source
 
+_Note: If you wish to contribute to the compiler, you should read
+[this chapter](https://rust-lang.github.io/rustc-guide/how-to-build-and-run.html)
+of the rustc-guide instead._
+
 ### Building on *nix
 1. Make sure you have installed the dependencies: