Add link to tls asciicast.

Closes #968.

man/mosquitto-tls.7.xml

@@ -26,6 +26,15 @@
 				you will experience difficult to diagnose errors.</para></note>
 	</refsect1>
 
+	<refsect1>
+		<title>Generating certificates</title>
+		<para>The sections below give the openssl commands that can be used to
+			generate certificates, but without any context. The asciicast at
+			<link
+				xlink:href="https://asciinema.org/a/201826">https://asciinema.org/a/201826</link>
+			gives a full run through of how to use those commands.</para>
+	</refsect1>
+
 	<refsect1>
 		<title>Certificate Authority</title>
 		<para>Generate a certificate authority certificate and key.</para>