diff --git a/tools/update-nixpkgs.rst b/tools/update-nixpkgs.rst
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index 0000000000000000000000000000000000000000..3888ecaa41b61a5b5e07f93b0f8f4b48ac54e210
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+++ b/tools/update-nixpkgs.rst
@@ -0,0 +1,8 @@
+To create a nice summary text to of what an update will change - to put in Merge Requests, for example - run::
+
+    nix-build -A morph -o result-before
+    update-nixpkgs
+    nix-build -A morph -o result-after
+    nix-shell -p nixUnstable
+    nix --extra-experimental-features nix-command store diff-closures ./result-before/ ./result-after/
+