Add link to previous BLAKE3 related blog post.

Author: rklaehn

src/app/blog/hashing-multiple-blobs-with-BLAKE3/page.mdx

@@ -129,6 +129,8 @@ The hazmat API gives you the ability to use the `Hasher` to compute the intermed
 
 But the API still focuses around the `Hasher`, so it still works only for computing data for *individual* blobs.
 
+<Note>We have written about the [new hazmat API](https://www.iroh.computer/blog/blake3-hazmat-api) previously</Note>
+
 ## Using the internal platform API
 
 So it looks like we have no choice but to dig deeper and see if we can implement this using existing internals.