Fix links for adding a new admonition kind

These files have been moved around.

Author: ehuss

tools/mdbook-spec/src/admonitions.rs

@@ -5,9 +5,10 @@
 //! 1. Modify the [`admonitions`] function below to include an icon.
 //! 2. Modify `theme/reference.css` to set the color for the different themes.
 //!    Look at one of the other admonitions as a guide.
-//! 3. Update `src/introduction.md` and describe what this new block is for
+//! 3. Update `src/conventions.md` and describe what this new block is for
 //!    with an example.
-//! 4. Update `docs/authoring.md` to show an example of your new admonition.
+//! 4. Update `dev-guide/src/formatting/admonitions.md` to show an example of
+//!    your new admonition.
 
 use crate::{Diagnostics, warn_or_err};
 use mdbook_preprocessor::book::Chapter;