diff --git a/src/nixos/nix-repo-url b/src/nixos/nix-repo-url
new file mode 100644
index 0000000..80a3f93
--- /dev/null
+++ b/src/nixos/nix-repo-url
@@ -0,0 +1,6 @@
+# Change nix repository overlay
+
+1. Edit `/etc/nixos/configuration.nix`
+2. Locate nixos repository overlay  at the beginning of the file.
+3. Change the branch name.
+4. `nixos-rebuild switch --upgrade`
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