Add note on deploying reference code

README.md

@@ -2,7 +2,9 @@
 
 This repository contains the reference implementation that accompanies [RFC 8391: _"XMSS: eXtended Merkle Signature Scheme"_](https://tools.ietf.org/html/rfc8391).
 
-This reference implementation supports all parameter sets as defined in the RFC at run-time (specified by prefixing the public and private keys with a 32-bit `oid`). Implementations that want to use compile-time parameter sets can remove the `struct xmss_params` function parameter.
+This reference implementation supports all parameter sets as defined in the RFC at run-time (specified by prefixing the public and private keys with a 32-bit `oid`). Implementations that want to use compile-time parameter sets can remove the `struct xmss_params` function parameter, and globally replace the use of its attributes by compile-time constants.
+
+Please note that this reference implementation is **intended for cross-validation and experimenting**. Deploying cryptographic code in practice requires careful consideration of the specific deployment scenario and relevant threat model. This holds perhaps doubly so for stateful signature schemes such as XMSS.
 
 _When using the current code base, please be careful, expect changes and watch this document for further documentation. In particular, `xmss_core_fast.c` is long due for a serious clean-up. While this will not change its public API or output, it may affect the storage format of the BDS state (i.e. part of the secret key)._