diff --git a/doc/building.md b/doc/building.md
index 4efa5ee..a9ccd32 100644
--- a/doc/building.md
+++ b/doc/building.md
@@ -44,6 +44,7 @@ Run this to install Redis - if you want to use Redis.
 
 Run this to install Postgres - if you want to use Postgres.
 
+    # install as root
     su
     apt-get install --no-install-recommends postgresql postgresql-client