env/linux-arm/scaleway: update notes

Change-Id: I5385e0bdc380b5849e3cc5db01bc9ffc8ddbce29
Reviewed-on: https://go-review.googlesource.com/c/build/+/170440
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/env/linux-arm/scaleway/README b/env/linux-arm/scaleway/README
index 516735d..00b9bcd 100644
--- a/env/linux-arm/scaleway/README
+++ b/env/linux-arm/scaleway/README
@@ -23,6 +23,8 @@
 
 	$ echo "<BUILDER KEY>" > /etc/gobuild.key > /root/.gobuildkey
 
+	$ apt-get remove --purge unattended-upgrades
+
 	$ systemctl enable /etc/systemd/user/rundockerbuildlet.service
 	$ systemctl start rundockerbuildlet.service