cli: Generate openssl.cnf snippet as file instead of writing it to terminal

certidude/templates/openssl.cnf

@@ -1,3 +1,6 @@
+# You have to copy the settings to the system-wide
+# OpenSSL configuration (usually /etc/ssl/openssl.cnf
+
 [CA_{{slug}}]
 default_crl_days = {{revocation_list_lifetime}}
 default_days = {{certificate_lifetime}}
@@ -38,3 +41,4 @@ emailAddress = optional
 basicConstraints = CA:FALSE
 keyUsage = nonRepudiation,digitalSignature,keyEncipherment
 extendedKeyUsage = clientAuth
+