Fix usage of {curves,key-exchanges}.pl in all.sh
diff --git a/tests/scripts/curves.pl b/tests/scripts/curves.pl
index bd13f52..f4942c6 100755
--- a/tests/scripts/curves.pl
+++ b/tests/scripts/curves.pl
@@ -17,9 +17,12 @@
#
# And any test suite with the wrong dependencies will fail.
#
-# Usage: curves.pl
+# Usage: tests/scripts/curves.pl
#
# This script should be executed from the root of the project directory.
+#
+# For best effect, run either with cmake disabled, or cmake enabled in a mode
+# that includes -Werror.
use warnings;
use strict;