Document how to use fbench with tokens (#4661)

Author: bratseth

en/performance/benchmarking-cloud.html

@@ -54,9 +54,20 @@ <h2 id="set-up-a-performance-test-instance">Set up a performance test instance</
 <p>At this point, the instance is ready, with data, and can be queried using data-plane credentials.</p>
 
 
+<h2 id="test-using-vespa-fbench-with-a-token-endpoint">Test using vespa-fbench with a token endpoint</h2>
+
+<p>To test using an API token endpoint instead of mTLS, use these options:</p>
+
+<pre>
+$ vespa-fbench -q query.txt -s 5 -H "Authorization: Bearer [your token]" -T /etc/ssl/certs/ca-bundle.crt -o out.txt "[token-endpoint]" 443
+</pre>
+
+<p>ca-bundle.crt is just the root certificates, nothing Vespa specific.</p>
+
 
 <h2 id="test-using-vespa-fbench">Test using vespa-fbench</h2>
-<p>The rest of the guide assumes the data-plane credentials are in working directory:</p>
+
+<p>The rest of the guide assumes we're using an mTLS endpoint and have data-plane credentials are in working directory:</p>
 <pre>
 $ ls -1 *.pem
   data-plane-private-key.pem