Fix usage of {curves,key-exchanges}.pl in all.sh
diff --git a/tests/scripts/key-exchanges.pl b/tests/scripts/key-exchanges.pl
index 46826c3..528812a 100755
--- a/tests/scripts/key-exchanges.pl
+++ b/tests/scripts/key-exchanges.pl
@@ -1,8 +1,25 @@
#!/usr/bin/perl
-# test that all configs with only a single key exchange enabled build
+# key-exchanges.pl
+#
+# Copyright (c) 2015-2017, ARM Limited, All Rights Reserved
+#
+# Purpose
+#
+# To test the code dependencies on individual key exchanges in the SSL module.
+# is a verification step to ensure we don't ship SSL code that do not work
+# for some build options.
+#
+# The process is:
+# for each possible key exchange
+# build the library with all but that key exchange disabled
#
# Usage: tests/scripts/key-exchanges.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;