diff --git a/test-doc.sh b/test-doc.sh
index d2aa2dc..7997153 100755
--- a/test-doc.sh
+++ b/test-doc.sh
@@ -10,6 +10,7 @@ done
 ## test the doc internal links
 ## https://github.com/remarkjs/remark-validate-links
 ## https://github.com/tcort/markdown-link-check
+## npm install -g remark-cli remark-validate-links
 set +e
 which remark >/dev/null 2>&1
 r="$?"
@@ -23,4 +24,4 @@ find . -type f -iname '*.md' | while read -r line; do
   remark -f -u validate-links "${line}"
 done
 
-echo "documentation OK"
\ No newline at end of file
+echo "documentation OK"