diff --git a/README.md b/README.md
index bc135db240c8a554ce9c43308c3826a053531db6..f6b07cf4f3580b88a41cd13d965146eaa9d61592 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,13 @@
 # Horizon Haskell Packages
+
+Put this in your `cabal.project`.
+
+```
+repository horizon
+  url: https://packages.horizon-haskell.net/
+  secure: True
+  root-keys:
+    272e995c7a74de109518100e1422193fe5e5971e52c92b98147c9355b47d7bb6
+    ea5c1bc0944dabe64d9d68c6813a8141d747cda042b870576d7af63a2326c31b
+    eb47482ddf51da1d3610094f5c57a626d42cfd7d9c248f53e23420b02b21c695
+```