Adds note on supported openssl versions for tls certificates. [skip ci]

Signed-off-by: Frederik Wedel-Heinen <[email protected]>

USAGE.md

@@ -196,6 +196,10 @@ to create QSC certificates replacing the key type "dilithium3" with any of the Q
 [signature algorithms supported](README.md#signature-algorithms).
 Of course, also any classic signature algorithm like "rsa" may be used.
 
+Note: While generating QSC certificates is supported with OpenSSL 3.0+, using 
+QSC CA's and server certificates is not supported in versions prior to OpenSSL 3.2.
+Refer to [Note on OpenSSL versions](README.md#note-on-openssl-versions).
+
 ### Setting up a (quantum-safe) test server
 
 Using keys and certificates as created above, a simple server utilizing a