link to new guides process

Author: Nadia Eghbal

CONTRIBUTING.md

@@ -27,7 +27,7 @@ There are also many ways you can directly contribute to the guides (in descendin
 * Add stories, examples, or anecdotes that help illustrate a point
 * Revise language to be more approachable and friendly
 * Translate guides into other languages
-* Propose a new guide (please open an issue to discuss before writing!)
+* Propose a new guide ([here's how](./docs/new-guides.md))
 
 Interested in making a contribution? Read on!