design/cryptography-principles: underscore that the list is sorted

Updates golang/go#32466

Change-Id: I5ad26960d48387b97331f050b86e2d4249c099ba
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/188518
Reviewed-by: Andrew Bonventre <andybons@golang.org>

design/cryptography-principles.md

diff --git a/design/cryptography-principles.md b/design/cryptography-principles.md
index 4e97b18..b6df115 100644
--- a/design/cryptography-principles.md
+++ b/design/cryptography-principles.md
@@ -53,6 +53,11 @@
 > expected that most functionality will be implemented by
 > third-party projects first, and that’s ok.
 
+Note that this is an ordered list, from highest to lowest
+priority. For example, an insecure implementation or unsafe API
+will not be considered, even if it enables more use cases or is
+more performant.
+
 ---
 
 The Go cryptography libraries are the `crypto/...` and