message: mention the plumbing
diff: @@ -42,3 +42,8 @@ example][hello_world], which has a number of comments explaining how
  things work.
  [hello_world]: https://github.com/salsa-rs/salsa/blob/master/examples/hello_world/main.rs
  +
  +## Digging into the plumbing
  +
  +Check out the [plumbing](plumbing.md) chapter to see a deeper explanation of the
  +code that salsa generates and how it connects to the salsa library.
  \ No newline at end of file
  