Added Conforming To section to EVP_KDF_TLS1_PRF documentation.

Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9008)

doc/man7/EVP_KDF_TLS1_PRF.pod

@@ -121,6 +121,10 @@ and seed value "seed":
  }
  EVP_KDF_CTX_free(kctx);
 
+=head1 CONFORMING TO
+
+RFC 2246, RFC 5246 and NIST SP 800-135 r1
+
 =head1 SEE ALSO
 
 L<EVP_KDF_CTX>,