Add uniform comment to setup.sh

Author: rffontenelle

scripts/setup.sh

@@ -6,6 +6,7 @@
 
 set -xeu
 
+# Fail earlier if required variables are not set
 test -n ${PYDOC_VERSION+x}
 test -n ${PYDOC_REPO+x}
 test -n ${PYDOC_LANGUAGE+x}