docs: [dialogflow] minor formatting (#6840)

* docs: minor formatting

PiperOrigin-RevId: 823067257

Source-Link: googleapis/googleapis@fc2a56a

Source-Link: googleapis/googleapis-gen@5aa33f9
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packages/google-cloud-dialogflow/protos/google/cloud/dialogflow/v2beta1/tool.proto

@@ -501,10 +501,12 @@ message Tool {
       // store to verify certificates. N.B. Make sure the HTTPS server
       // certificates are signed with "subject alt name". For instance a
       // certificate can be self-signed using the following command,
+      // ```
       //    openssl x509 -req -days 200 -in example.com.csr \
       //      -signkey example.com.key \
       //      -out example.com.crt \
       //      -extfile <(printf "\nsubjectAltName='DNS:www.example.com'")
+      // ```
       bytes cert = 2 [(google.api.field_behavior) = REQUIRED];
     }