diff --git a/README.md b/README.md
index bf1038c1d1abc1215fb16ff18bf43b87dcbf765c..905846013a2040f700a7bcb7aae2c2e35a7ad4f4 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,6 @@
+#reference:
+- https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/blob/master/docs/executors/virtualbox.md
+
 # pending issue (imho):
 - https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1121
 - https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/merge_requests/110