diff --git a/Makefile b/Makefile
index c258278..0584fa0 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,5 @@
-# See the documentation on how to run the tests.
+# See the documentation on how to run the tests:
+# https://vdirsyncer.pimutils.org/en/stable/contributing.html
 
 # Which DAV server to run the tests against (radicale, xandikos, skip, owncloud, nextcloud, ...)
 export DAV_SERVER := skip