diff --git a/README.md b/README.md
index 66ccc17..eedad9f 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,7 @@
 # Guidelines
 
 - Scripts must use `set -euo pipefail`
+- All work should be done in a temporary directory (`mktemp -d`)
 
 ## Building