docs(book): Update information on new layering strategy

docs/src/nixery.md

@@ -7,8 +7,11 @@ contain packages from the [Nix][] package manager. Images with arbitrary
 packages can be requested via the image name.
 
 Nix not only provides the packages to include in the images, but also builds the
-images themselves by using an interesting layering strategy described in [this
-blog post][layers].
+images themselves by using a special [layering strategy][] that optimises for
+cache efficiency.
+
+For general information on why using Nix makes sense for container images, check
+out [this blog post][layers].
 
 ## Quick start
 
@@ -65,13 +68,11 @@ availability.
 
 ### Who made this?
 
-Nixery was written mostly by [tazjin][].
-
-[grahamc][] authored the image layering strategy. Many people have contributed
-to Nix over time, maybe you could become one of them?
+Nixery was written by [tazjin][], but many people have contributed to Nix over
+time, maybe you could become one of them?
 
 [Nixery]: https://github.com/google/nixery
 [Nix]: https://nixos.org/nix
+[layering-strategy]: https://storage.googleapis.com/nixdoc/nixery-layers.html
 [layers]: https://grahamc.com/blog/nix-and-layered-docker-images
 [tazjin]: https://github.com/tazjin
-[grahamc]: https://github.com/grahamc

docs/src/under-the-hood.md

@@ -51,7 +51,8 @@ does not allow uppercase characters, so the Nix code will translate something
 like `haskellpackages` (lowercased) to the correct attribute name.
 
 After identifying all contents, Nix determines the contents of each layer while
-optimising for the best possible cache efficiency.
+optimising for the best possible cache efficiency (see the [layering design
+doc][] for details).
 
 Finally it builds each layer, assembles the image manifest as JSON structure,
 and yields this manifest back to the web server.
@@ -103,3 +104,4 @@ to run the image produced by Nixery.
 
 [gcs]: https://cloud.google.com/storage/
 [signed URLs]: https://cloud.google.com/storage/docs/access-control/signed-urls
+[layering design doc]: https://storage.googleapis.com/nixdoc/nixery-layers.html