update contributing docs

Author: rosahbruno

CONTRIBUTING.md

@@ -10,8 +10,8 @@ Before you dive into technical details, take a moment to read our
 Any form of communication from chat rooms and mailing lists to code comments
 is expected to follow this code of conduct, so that all can enjoy working on Glean.js.
 
-Glean.js' developer document lives in the [`docs/`](https://github.com/mozilla/glean.js/tree/main/docs/index.md)
-folder in this repository and Glean.js' user documentation lives in [The Glean Book](https://mozilla.github.io/glean/book/index.html).
+Glean.js' developer document lives in the [`docs/`](https://github.com/mozilla/glean.js/tree/main/docs/README.md)
+folder in this repository and Glean.js' user documentation can be found at [mozilla.github.io/glean.js/](https://mozilla.github.io/glean.js/).
 
 Here's the [guide](https://github.com/mozilla/glean.js/blob/main/docs/guides/getting_started.md) to get you started!