[ci skip] Add a note about password storage in CI_Encryption docs
I saw at least 2 occurrences of encryption instead of hashing
being used for password storage during the past week ...
diff --git a/user_guide_src/source/libraries/encryption.rst b/user_guide_src/source/libraries/encryption.rst
index 5f0979d..0c34760 100644
--- a/user_guide_src/source/libraries/encryption.rst
+++ b/user_guide_src/source/libraries/encryption.rst
@@ -2,6 +2,11 @@
Encryption Library
##################
+.. important:: DO NOT use this or any other *encryption* library for
+ user password storage! Passwords must be *hashed* instead, and you
+ should do that via PHP's own `Password Hashing extension
+ <http://php.net/password>`_.
+
The Encryption Library provides two-way data encryption. To do so in
a cryptographically secure way, it utilizes PHP extensions that are
unfortunately not always available on all systems.