update contributing to show how to build the docs

The contributing guide referenced a script that was deleted in
1271bb4de0c0 so it wasn't possible to follow the contributing guide
successfully prior to contributing doc improvements.

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index eb7374ee6686cae341265dbca8954b9e71b12bfa..ed260e51a26c12e7e059fd112d3de2fb853e1501 100644 (file)
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -109,13 +109,16 @@ and [merges][mergequeue] it into Cargo's `master` branch.
 
 To contribute to the documentation, all you need to do is change the markdown
 files in the `src/doc` directory. To view the rendered version of changes you
-have made locally, run:
+have made locally, make sure you have `mdbook` installed and run:
 
 ```sh
-sh src/ci/dox.sh
-open target/doc/index.html
+cd src/doc
+mdbook build
+open book/index.html
 ```
 
+To install `mdbook` run `cargo install mdbook`.
+
 
 ## Issue Triage